i894. CEPHALOPOD BEGINNINGS. 425 



British Museum, that two species of Orthocevas (a genus universally 

 ascribed to the Nautiloidea) did indeed possess very visible traces of 

 a protoconch in the form of shrivelled masses of calcareous matter, 

 which overlaid and obscured the cicatrix. The shrivelling was sup- 

 posed by Hyatt to indicate that the protoconch in these forms was 

 only slightly calcified, that, in short, it was chiefly formed of 

 conchiolin. This would similarly account for its destruction in so 

 many individual cases, and for its final complete disappearance in the 

 subsequent history of the Nautiloidea. Upon this theory the gap 

 assumed by Branco and Barrande to exist between Ammonoidea and 

 Nautiloidea was to a certain extent bridged. " There is," wrote 

 Hyatt, " convincing evidence in the structures of [certain] Cambrian 

 shells that the Ammonoidea, with their distinct embryos, arose from 

 the orthoceran stock, and passed through a series of forms, in times, 

 perhaps, preceding the Cambrian, which were parallel to those 

 characteristic of genetic series among Nautiloidea, viz., straight, 

 arcuate, gyroceran, and nautilian." Six years later, in his magnificent 

 monograph on the Genesis of the Arietidae (12), Hyatt considered 

 that the accumulated evidence had become yet more convincing ; one 

 observation of special importance was that the longitudinal striae, 

 which are so characteristic of many young nautiloids, were believed 

 to pass from the conch itself onto the surface of the shrivelled mass 

 which Hyatt claimed to be the protoconch. 



Now, since so much stress has been laid, by Hyatt and others, 

 on these observations, it behoves us to consider them with great 

 attention. Fortunately the critical specimens are preserved in the 

 British Museum, so that it has been possible for my colleague, 

 Mr. G. C. Crick, and myself to subject them to a prolonged examina- 

 tion with the aid of the microscope. I am compelled, before pro- 

 ceeding with this article, to formulate our conclusions, which have 

 reference to the figures on page 10 of " The Genesis of the Arietidae " : — 



Figures 1-3. This specimen shows absolutely no trace of longitu- 

 dinal striae ; therefore it is impossible for longitudinal striae to pass 

 onto the so-called protoconch, a statement based solely on the evidence 

 of this specimen. On the other hand, it shows distinct traces of con- 

 centric striae, which would doubtless have been more distinct had the 

 specimen not been rolled and rubbed. There is no great distinction 

 in colour or texture between the so-called protoconch and the rest of 

 the shell. There are, however, clear signs that the shell has been 

 flaked off from the end, and it seems perfectly possible that it once 

 extended over the so-called protoconch. There is absolutely no 

 evidence that the supposed shrivelled remains of the protoconch rest 

 upon the cicatrix, or that they extend over the apical plate ; on the 

 contrary all the appearances suggest that this wrinkled mass passes 

 up from inside the cicatrix, and that it is merely a plug, or infilling of 

 secondary calcite deposited within the shell during the life of the 

 animal. 



Figures 4 and 5 are more correct, but the distinctness of the 

 protoconch is certainly exaggerated. There is, indeed, a slight con- 

 striction, but there is no sign of shrivelling. 



