18/8> ] SHELLS OF CEPHALOPODS. 973 



nati of Bohemia led the exemplary and acute observer Barrande to 

 conceive that a arger proportion of the soft parts had been therein 

 lodged than is the case in the slender simple siphons of other TetrT 

 bnmchiates, and m all that are of later date, when the partial office 

 of die siphon is reduced to reception of a trace of the vascular system 



Produce both the "saucer" and "cup" of Calypeopsis, wfth the 

 resultant "false bottoms" or septa, as in FermetusiJ. 1 p . 9o6) 

 and an analogue, if not parallel, of Endoceras would ensue h 



Hyatt has noted the resemblance of the cup-like internal chambers 

 oiBeatricea to a line of siphonal c*eca. The protoconch (primal 

 shell, nucleus, ovisac, embryo, &c, fig. 5, a) has been determined, 



Fig. 5. 



Spinda australis. 

 Protoconch and protosiphon, with following chambers, magnified. 



described, and figured by De Blaiuville (in Spirula 1 ) ; also by 

 Sandberger 2 , by Barrande 3 , and, with exemplary care and patience, by 

 Alpheus Hyatt 4 , in various species of tetrabranchiate shells. The 

 results by no means support any doubt as to the externality of the 

 shells of the Ammonitidse, or at all support the notion of their closer 

 affinity to Spirula than to Nautilus. 



The supposed well-marked distinction between the protoconch of 

 Ammonites and that of Nautilus is mainly due, as Hyatt has shown, 

 to its decadence in Nautilus after the deuteroconch (fig. 5, b), or suc- 

 cessional shell-chamber, is formed— the primal communication with 

 the protoconch being then indicated by a linear cicatrix on the first 

 septum 6 . On this indication of the original existence and attach- 

 ment of the protoconch I may remark, that when the young Nau- 

 tilus, becoming too big for its first shell, moved on to make another, 

 part of that " making " encroached upon the space which the young 

 had traversed, and reduced it more or less to the shape of a chink 

 or scar. But it must not be concluded that this chink preexisted 

 to the progress, and that the young crept or squeezed through such 

 chmk, as when Mr. Hyatt writes of "the central scar which marks 

 the former aperture through which the animal probablv passed into 

 the fundus of the first whorl" 6 . It is only under such impression 

 that it becomes " difficult to account for the passage of the large 



1 Op. cit. 



2 Oberheesische Gesellschaft fiir Natur und Heilkunde, 1858. 



3 Op. cit. 



* Fossil Cephalopods of the Museum of Comparative Zoology.— Embry- 

 ology (8vo, Cambridge, Mass.), vol. iii. no. v. 1872. 

 s Ibid, p. 64. 6 pitf, „ 7a 



