Sirenites（Sirenitinae）?vs? Yakutosirenites（?Arpaditinae）

美女神菊石屬 vs? 雅庫(kù)特美女神菊石屬

All ammonoids assigned in this paper to the genus Sirenites have a compressed discoconic shell with moderately embracing whorls overlapping approximately half of the height of the preceding whorl.? The ornamentation on the flanks is composed of densely spaced crescentic ribs with five spirals of nodes:umbilical, two lateral, ventrolateral, and ventral.? The ribs begin from the umbilical shoulder and terminate with the nodes of the ventral spirals;? they tend to expand toward the venter.? This feature was already mentioned in the first description of the senticosi group (Mojsisovics, 1893, p. 727).? The ventrolateral spiral of nodes lying on the ventral shoulder, the ribs split into two shorter ribs, sharply bent forward and reaching the ventrolateral spiral of nodes.? The splitting is observed at the middle and later growth stages (shell diameter more than 10?15 mm), either in every second rib or in each rib, so the number of nodes of the ventral spiral is 1.5–2 times higher than that of the ventrolateral spiral.? The ribs, unlike in the genus Yakutosirenites, are maintained at the later growth stages(Plate I, figs.? 3, 8). On either side of the midventral groove, there are either raised keels with elongated frequently spaced oblique nodes of ventral spirals (Plate I,fig.? 1c) or densely spaces pointed carinate nodes, lowering toward the groove (Plate I, fig. 2c).

本文所確定的Sirenites菊石屬都有一個(gè)壓縮的盤狀殼，其螺旋高度約為前一螺旋高度的一半。側(cè)翼的紋飾由密集間隔的新月形肋組成，肋上有五個(gè)螺旋狀結(jié)節(jié):臍部的、兩個(gè)側(cè)面、腹側(cè)部和腹部。肋從臍肩開(kāi)始，終止于腹部螺旋結(jié)節(jié);它們傾向于向腹部擴(kuò)張。這一特征已經(jīng)在第一次描述senticosi群時(shí)被提及(Mojsisovics, 1893, p. 727)。腹側(cè)部螺旋狀結(jié)節(jié)位于腹肩部，肋分裂為兩根較短的肋，急前彎，并到達(dá)腹側(cè)部螺旋狀結(jié)節(jié)。在生長(zhǎng)的中后期(殼直徑大于10 ~ 15 mm)，要么是每隔一個(gè)肋要么是在每一肋都有分裂，因此腹部螺旋的結(jié)節(jié)數(shù)是腹側(cè)部螺旋的1.5-2倍。與Yakutosirenites屬不同的是，肋在生長(zhǎng)后期保持不變(Plate I, figs.?3, 8)。在腹中溝的兩側(cè)，要么有凸起的脊，并有伸長(zhǎng)而常間隔的腹部螺旋斜節(jié)(Plate I,fig.? 1c)，或密集的、向凹槽降低的空間指向隆凸的結(jié)節(jié)(Plate I，fig 2c)。

?In the shape of the nodes of the ventral spiral, this ammonoid group is readily distinguished from the genus Yakutosirenites, in particular, from Y. pentastichus (Vozin), in which the ventral spiral possesses widely spaced large spines, when the shell matrix is preserved (Plate I,fig. 6a), and on the mold, rounded, elongated ridges(Plate I, figs. 4a, 4b).??

在腹部螺旋結(jié)節(jié)的形狀上，Sirenites很容易與Yakutosirenites屬區(qū)分開(kāi)來(lái)，特別是與Y. pentastichus (Vozin)區(qū)分開(kāi)來(lái)。當(dāng)后者殼的母體被保存下來(lái)時(shí)，可以看到外旋環(huán)腹部螺旋擁有寬間隔的棘狀突起 (Plate I,fig.? ?6a)，并在體型上，有圓形，細(xì)長(zhǎng)的脊(Plate I, figs.? ?4a, 4b)。

Plate I. Ammonoids of the genera Sirenites and Yakutosirenites from the lower–upper Carnian boundary beds of Northeast Asia (northern Verkhoyansk Region, Darky River; northern Okhotsk Region, Vtoraya Sentyabrskaya River; Kotelnyi Island, Tikhaya River). In all cases: (a) lateral view, (b) apertural view, (c) ventral view. All sizes are natural, except for the specially mentioned cases. The collection of illustrated ammonoids is housed in the Monographic Department of Central Siberian Geological Museum (TsSGM) in the Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk), coll. no. 2080. (1, 8) Sirenites ovinus Tozer, lower Carnian, upper part of the armiger Zone?lower Carnian, lower part of the pentastichus Zone: (1) specimen no. 1/2080, northern Okhotsk Region, basin of the Yana Okhotskaya River, Vtoraya Sentyabrskaya River, Outcrop C-2, Bed 3, 2 m above the base; (8) specimen no. 6/2080; northern Verkhoyansk Region, Darky River, Outcrop 52, Bed 8, 3.5 m above the base; (2, 3) Sirenites senticosus (Dittmar), lower Carnian, armiger Zone: (2) specimen no. 2/2080, ×3, Kotelnyi Island, Tikhaya River, loc. 06-8, Bed 4, 11 m above the base; (3) same specimen put together with the subsequent whorl in argillaceous limestone with small ammonoids; dashed lines indicate specimens and imprints of Yakutosirenites armiger (Vozin) sp. juv.; solid arrows show Sirenites senticosus (Dittmar) sp. juv; (4–6) Yakutosirenites pentastichus (Vozin), lower Carnian, pentastichus Zone: (4) specimen no. 3/2080, northern Okhotsk Region, basin of the Yana Okhotskaya River, Vtoraya Sentyabrskaya River, Outcrop С-2, Bed 3, 4.5 m above the base; (5) the same specimen, ×3; (6) specimen no. 4/2080, in a clayey-carbonate concretion, the same locality, Bed 3; 8.7 m above the base; (7, 11, 12) Sirenites sp. indet., lower Carnian, armiger Zone: (7) specimen no. 5/2080, Kotelnyi Island, Tikhaya River, loc. 06-8, Bed 4; 5 m above the base; (11) specimen no. 9/2080, northern Okhotsk Region, basin of the Yana Okhotskaya River, Vtoraya Sentyabrskaya River, Outcrop С-2, Bed 1; 40.5 m above the base; (12) specimen no. 10/2080, (12a and 12b) lateral views, the same locality, Bed 1; 43.5 m above the base; (9) Sirenites cf. senticosus (Dittmar), lower Carnian, armiger Zone, specimen no. 7/2080, northern Verkhoyansk Region, Darky River, Outcrop 52, Bed 7; 4 m above the base; (10) Striatosirenites cf. dromas (Dittmar), photograph from a latex cast, lower Carnian, armiger Zone, specimen no. 8/2080, northern Verkhoyansk Region, Darky River, Outcrop 52, Bed 8; 2.5 m above the base.

參考：The Yakutosirenites armiger Ammonoid Zone of Northeast Asia as a Reference Level of the Boreal-Tethyan Correlation of the Lower Carnian.

前粗菊石屬 Protrachyceras

殼體半內(nèi)卷至近內(nèi)卷，呈扁餅狀。腹部具腹溝,溝旁各有一排瘤。殼表具有許多橫肋,每一肋上附有排列規(guī)則的瘤,橫肋常分叉或插入?？p合線為亞菊石式，鞍部也發(fā)生微弱的褶皺。

粗菊石屬 Trachyceras Mojsisovics，1893

殼體半外卷到近內(nèi)卷，厚餅狀到扁餅形。腹部穹圓，有明顯腹中溝，兩旁的腹棱上有兩排瘤。側(cè)面飾有簡(jiǎn)單的、二分的、微彎的肋紋。肋上有若干排成旋轉(zhuǎn)狀的瘤節(jié)?？p合線為亞菊石型，每一外側(cè)面有兩個(gè)分齒不很長(zhǎng)的側(cè)葉。

對(duì)比：前粗菊石的腹溝兩旁的棱上只有一排瘤，其為兩排。

副粗菊石屬?Paratrachyceras?Arthaber, 1914

亞科：Protrachyceratinae

The whorl section is compressed with broadly arched flanks which bear flat ribs that project forward near the venter. The ribs are much broader than the interrib spaces.?The ribs cross the venter forming? forward projected chevrons within a ventral? furrow.?The ribs are broadest near the ventral region of the flanks and narrow slightlywhere they are projected forward and over? the venter.?

Remarks：As well as one can interpret? these specimens, the main morphological features-that is the compressed whorl section, degree of involution, the nature of the ribs, the absence of nodes or tubercles and the?grooved venter-indicate affinities to Trachyceras (Paratrachyceras).?In most species of this genus the ventral groove is smooth, the ribs not crossing the venter.?The only exception to this that I have been able to? discover is the specimen described and illustrated by Arthaber (1914, p. 137, pl. 16,? fig. 1) as T. (Paratrachyceras) regoledanum (Mojsisovics) from an Upper Ladinian horizon in Turkey.? This specimen has the ribs passing over the venter in the same fashion as that of the Thailand specimen illustrated here on?figures 1,2.? Arthaber's? specimen appears to be quite similar to the Thailand specimens in terms of conch shape, involution, and type of ribbing except that there are some nodes on the ribs.?Other illustrations of this species, unfortunately, do?not show the nature of the venter.

旋環(huán)部分被寬拱的側(cè)翼壓縮，側(cè)翼支撐著靠近腹部前伸的扁平肋。肋比肋間隙寬得多。肋穿過(guò)腹面，在腹面溝槽內(nèi)形成向前投影的v形。肋在側(cè)翼的腹側(cè)區(qū)域附近最寬，在向前突出并于腹部的地方略微狹窄。

備注: 除了可以解釋這些標(biāo)本外，主要的形態(tài)學(xué)特征——壓縮的旋環(huán)、內(nèi)卷程度、肋的性質(zhì)、沒(méi)有nodes或tubercles以及有具溝的腹部——表明與Trachyceras (Paratrachyceras)有親緣關(guān)系。在本屬的大多數(shù)種的腹溝是光滑的，肋不穿過(guò)腹部。所能發(fā)現(xiàn)的唯一例外是Arthaber (1914, p. 137, pl. 16，圖1)描述和說(shuō)明的來(lái)自土耳其上拉底地區(qū)地平線的T. (Paratrachyceras) regoledanum (Mojsisovics)標(biāo)本。這個(gè)標(biāo)本的肋穿過(guò)腹部的方式與figures 1,2.所示的泰國(guó)標(biāo)本相同。Arthaber的標(biāo)本在殼形、內(nèi)卷和肋類型方面似乎與泰國(guó)的標(biāo)本非常相似，除了肋上有一些nodes。不幸的是，這個(gè)物種的其他插圖并沒(méi)有顯示腹部的性質(zhì)。

奧地利粗菊石屬? Austrotrachyceras

亞科：Trachyceratinae

None show suture lines. All show two spirals of tubercles adjacent to the ventral sulcus flanked by a smooth band. Clearly shown is the principal generic character of Austrotrachyceras, namely feeble projection of growth lines and tubercle spirals on the venter.

沒(méi)有顯示縫合線。所有圖均顯示兩螺旋狀排列的結(jié)節(jié)毗鄰腹溝，腹溝兩側(cè)有平滑帶。主要的一般特征，即生長(zhǎng)線和結(jié)節(jié)螺旋在腹部上的微弱突起被清楚地顯示。

參考：CANADIAN TRIASSlC ANlMONOID FAUNAS，1994