A. S. Foord — On the Genus Piloceras. 545 



Whatever the functions of the endosiphon may have been, I do 

 not imagine that it played such an important j)art in the vital 

 economy of the animal as did the same organ in Actinoceras. The 

 large endosiphon in the latter gave off tubuli which passed through 

 the membranous walls of the siphuncle by means of foramina.^ Sir 

 Eichard Owen conjectured that these tubuli served "for the passage 

 of blood-vessels to the lining membrane of the air-chambers."* At 

 any rate, a vital connection was maintained between the endosiphon 

 and each of the septal-chambers in Actinoceras, which, was wanting 

 in Piloceras. 



The genus Piloceras may now be thus redefined : — 



Shell more or less broadly conical ; slightly curved ; somewhat 

 compressed laterally ; elliptical in section. Septa rather numerous. 

 Siphuncle formed by the prolongation and conjunction of the necks' 

 of the septa ; marginal ; very large ; partaking of the curvature of 

 the shell ; provided internally with one or more conical, or funnel- 

 shaped sheaths, which are united at the top with its margin. These 

 sheaths apparently communicated with one another by means of the 

 endosiphon, which perforates the apex of the siphuncle- The 

 endosiphon originated in one of the earlier of the septal-chambers, 

 if not in the initial chamber itself.^ 



Five species of Piloceras have now been described, viz : — 



F. amphim, Dawson. 

 F. explanatory Whitfield. 



F. invaginatum, Salter. 

 F. Canadense, Billings. 

 F. IVortheni, Billings. 



Thus, nearly all the structures in the siphuncle and some of those 

 of the chambered portion of the shell of Piloceras described by 

 Dawson and Hyatt are demonstrable in the splendid series of 

 specimens brought together by Mr. Peach. 



The great desideratum now is to obtain a specimen which will 

 disclose the connection between the apex of the siphuncle and the 

 chambered part of the shell. For this purpose a tolerably perfect 

 specimen would be required. Perhaps some of the material so 

 ably dealt with by Professor Whitfield may supply the want ? One 

 can scarcely expect to find sufficiently perfect specimens in the 

 Durness rocks. 



From a geological point of view Filacer as is interesting on account 

 of its association in Scotland and in eastern North America with a 

 little group of fossils in which several species appear to be common 

 to both countries. 



^ These are beautifully preserved in many examples of Actinoceras in the British 

 Museum (Nat. Hist.). 



^ Palaeontology, '2nd ed. 1861, p. 102. See also L. Saemann, Ueber die Nautiliden, 

 Palseontographica, Band iii. 1845, p. 121, Tab. xviii. 



^ Called "funnels" by Prof. Hyatt. " Siphonalduten " of the Germans; 

 " goulots " of the French. 



* Hyatt in his definition of Filoceras (loc. cit. p. 266) states that it is "often 

 annulated," but this is evidently an inadvertence, because the outer shell was 

 unknown when he wrote, and remained so until the specimens described by Prof. 

 Whitfield saw the light, and these showed only ' ' a few transverse wrinkles of 

 growth." He probably had in his mind the detached siphuncles, which have an 

 annulated appearance caused by the adherent remains of the septa. 



DECADB III. VOL. IV. NO. XII. 35 



