AUG 17 1893 



r 71 



IV. On the Mnscnlar Attachment of the Animal to its Shell in some Fossil Cephalo])oda 

 [Ammonoidea). By G. C. CmcK, F.G.S., F.Z.S., of the British Iliiseum [Natural 

 Sistory). [Communicated l»j the Piiesident.) 



(Plates 17-20.) 



Read 3rfl February, 1S!)8. 



INDIC^ITIONS of the muscular attachment of the animal to its shell have been 

 tigured in not a few Nautiloids, but comparatively few Ammonoids have been recorded 

 in which what has been believed to be the remains of this attachment has been iigured 

 and described. Of these the best known are Oppel's figures of three examples of 

 Ammonites steraspis* from the Lithographic Stone of Bavaria, iiublished in 1863, in 

 which the body-chamber of each is shown to be traversed by a fine curved line, the 

 relation of which to the animal was not, however, indicated by the author. 



In 1870, Trautschold f figured a specimen of Ammonites hicurnatus, exhibiting what 

 he considered to be the impression of the muscular attachment of the animal, but this 

 figure differs considerably from Oppel's figiu'cs. 



In the following year, Dr. W. Waagen % published his important paper, " Ueber die 

 Ansatzstelle der Haftmuskeln beim Nautilus und Ammonoiden," in which he expressed 

 his opinion that the " shell-muscle " in the Ammonoidea was attached to the inner 

 (umbilical) portion of the lateral area of the whorl. He believed the curved line 

 figured by Oppel on the body-chamber of Ammonites steraspis to be a trace of the 

 " annulus," and probably also of the shell-muscle, and, reproducing one of Oppel's 

 figures, he completed by a dotted line what he considered to be the form of the shell- 

 muscle. This interpretation of Oppel's figures has been accepted by most authors. 



In 1879, Eck § figured and described a small septate fragment of Ceratites semipartitus 

 from the Upper Muschelkalk of Schwielierdingen, near Stvittgart, Avhich he thought 

 showed not only the appearance of the surface of the mantle (the so-called " epidermids "), 

 but also the impression of the annulus. The specimen was merely an internal cast of 

 five chambers, and on the surface of the cast of each chamber there was a depressed zone 

 with a finely-pitted surface, occupying on the siphonal region the middle two-thirds, and 

 becoming much narrower on the side of the whorl ; in two of the chambers a groove was 

 also present on the antisiphonal area. 



* Pal. Mittheil. p. :2.j1, pi. Ixis. figs. 1, 2, & 6 (1863). 

 t Bull. Soc. Nat. Moscou, vol. xliii. pp. 301-306 (1870). 

 t Pateontographica, vol. xvii. pp. 185-210, pis. xxsis. & xl. (1871). 

 § Zeitschr. deutsch. geol. Gesell. vol. xxxi. p. 276, pi. iv. figs. 5 a-d (1879). 

 SECOND SERIES. — ZOOLOGY, VOL. VII. 11 



