102 Prof. Nicholson — On Endoceras in Britain. 



III. — On the Occtterbnce of the Genus Endoceras in Britain. 



By H. Alletne Nicholson, M.D., D.Se., M.A., Ph.D., F.E.S.E., 

 Professor of Natural History and Botany in TJniyersity College, Toronto. 



THE genus Endoceras was proposed by Hall (PaL N. York, vol. i., 

 p. 58) for a group of Orthocerata; haA'ing "a large siphuncle, 

 mostly lateral or excentrio, marked or ridged on the outer surface by 

 the septa, which, from their oblique direction, give it the appearance 

 of a tube with spiral lines. Within this siphuncle are one or more 

 very elongated conical tubes, often one within the other to the num- 

 ber of four or five." The leading point, then, in the definition of 

 Endoceras is the possession of a multiple siphuncle, composed of two 

 or more concentric tubes placed one within the other, each tube 

 having the form of an elongated cone. As to the existence of this 

 peculiar structure, no doubt can be entertained; but very remarkable 

 views have been put forward by Hall as to the true nature of these 

 internal tubes. The tubes which are contained within the siphuncle 

 are perfectly smooth and very thin, and they are believed, by the 

 above-mentioned eminent palEeontologist, to be receptacles within 

 which the young shells were retained for a certain length of time. 

 Upon this belief, they are termed by Hall "embryo-sheaths"; and 

 it is asserted that they are found to contain young Endocerata in 

 various stages of development, sometimes exhibiting septa and a 

 siphuncle, and sometimes in the form of simple tubes, without either 

 of these structures. As to the further development of these supposed 

 young shells, Hall seems to have inclined to the view that the young 

 Endoceras enlarged within the parent shell until the latter perished ; 

 but he seems to have also thought it possible that the young shells 

 were expelled from the siphuncle of the parent-shell whilst still im- 

 mature. It seems difficult to give any adequate explanation of the 

 phenomena described by Hall, and it is at the same time very difficult 

 to accept the views above stated. We know, however, so little of 

 the functions of the siphuncle, especially in the extinct group of the 

 Orthoceratida, that it is impossible to declare dogmatically that 

 Hall's explanation of the phenomena may not be correct. Other 

 observers, however, regard the supposed young Orthocerata, within 

 the so-called " enibryo-sheath," as having fallen accidentally into the 

 cavity of the siphuncle, after the death of the animal ; whilst the 

 embryo-sheath is looked upon as the cast of the internal cavity of 

 the siphuncle. Others, again, regard the embryo-sheaths as being of 

 the nature of funnel-shaped diaphragms placed one within the other 

 within the cavity of the siphuncle. This latter view, however, can 

 hardly be correct, since the embryo-tube is described as not being 

 connected with the walls of the siphuncle, whilst it commonly occurs 

 detached from the shell to which it belongs. The former view, also, 

 must be rejected, since it could at best but apply to cases in which 

 only one " embryo-tube " was present. 



Several species of Endoceras have been described by Hall from the 

 Black River and Trenton Limestones, and some of them attained 

 gigantic dimensions. No species of this genus, so far as I am aware, 



