THIRD, OR VERMICERAN BRANCH. 149 



One specimen in the Museum of Comparative Zoology has somewhat deeper 

 channels than is usual in this species, but is otherwise quite similar to the raricos- 

 tatus-like variety (Plate I. Fig. 19, 20). Quenstedt identifies this variety with 

 Am. kridioides {kridion) in his " Ammoniten der Schwabischen Jura," but from 

 this species it differs essentially, if we are right in our selection of the form to 

 which the name Amm. kridion, Oppel, has been applied. Undoubtedly there is a 

 close resemblance between this species and raricostatum, on the one hand, and Am. 

 kridioides on the other. The young and the channels separate it from the former, 

 and the great breadth of the whorls, channels, caloceran pilse, and sutures, from 

 the latter. The raricostatus-like form of the whorl and pilse, and absence of 

 tubercles, distinguish it from what we consider to be the true kridion. Zieten's 

 figure of a specimen from Kalthenthal, near Stuttgardt, has exactly the aspect 

 of this species, and though the abdomen looks somewhat broader in Zieten's sec- 

 tion the pilse have no tubercles. It is more like this species than any form of 

 kridion or kridioides, if the figure is accurate. 



Caloceras laqueoides, Hyatt. 



Amm. sinemuriense, Fraas. 



In this specimen, now in the collection of the Museum at Stuttgardt, found, 

 according to Fraas, in the Angulatus bed, there is a most singular mingling 

 of the characteristics of Zaqiieum with the peculiar pilse of Coroniceras Bucklandi, 

 var. sinemuriense. 



The young and adult whorls are smaller and more numerous than those of 

 sinemuriense, and like those of laqueum. The abdomen, however, has narrow 

 channels, and many of the pilse in the adult have large tubercles somewhat 

 thrown back, which give them the aspect of the undivided pilse of sinemuriense. 

 Between these there are usually two or more of the linear pilse of one variety of 

 laqueum, and the tubercles when covered by the shell do not extend into spines, 

 but remain mere tubercles. 



In old age or on the last whorl of this specimen, which may perhaps be 

 prematurely old, the intermediate pilae alone are found, the stout tuberculated 

 simuriense-like pilae having become obsolescent. At this time the form and 

 characteristics of the whorl are precisely as in laqueum, except the channels ; 

 these still remain very much shallower. Upon the whole, therefore, it is prob- 

 able that this may be a distinct species. Together with others, it shows that 

 Caloceras may have forms which are the morphological equivalents of the tuber- 

 culated, keeled, and channelled progressive forms of Vermiceras, Coroniceras, 

 and Asteroceras. 



