72 On the Shell-structure of Spirifer cuspidatus S^c. 



the singular correspondence between the patchtj distribution of 

 the perforations in Nos. 2, S, 4 and that which is characteristic 

 of Syringothijris (No. 1)— a correspondence which is the more 

 sio-nificant as I have not elsewhere encountered this peculiarity. 

 °0n shcing across my perforated Millecent specimens (No. 4) 

 in the direction indicated by Prof. Winchell's figure, the internal 

 structure of one of them proved to be sufficiently well preserved 

 to show most distinctly the transverse lamina (fig. 3, tr.) con- 



Fig. 3. Transverse section of Syringothyris from Millecent, from a drawing 

 by Mr. Davidson : I, I, dental plates ; tr, transverse lamina; t, incom- 

 plete tube. 



Fig. 4. Transverse section of true Spirifer cuspidatus from Millecent, from 

 a drawing by Mr. Davidson : I, I, dental plates. 



necting the dental plates {I, I), with its projecting pair of 

 lamellae forming the nearly complete tube {t) characteristic of 

 the typical Syringothyris (figs. 1, 2), to which genus, therefore, 

 these shells are obviously to be transferred. 



Nothing, then, remained save to subject the imperfo7-ate shell 

 of the true Spirifer cuspidatus (No. 5) to the same crucial test; 

 and on carrying a section through this specimen in precisely the 

 same direction (ab), it proved that its dental lamiuge (/, /, fig.4) 

 are unconnected by any transverse plate, and that there is no 

 vestige whatever of the characteristic tube of Syringothyris. 



Thus, then, the remarkable fact is incontestably established 

 that there is an exact isomoiyh of Spii'ifer cuspidatus, not distin- 

 guishable from it by external conformation, but generically 

 differentiated by a very marked peculiarity of internal structure, 

 of which peculiarity the perfoi*ated structure of the shell seems 

 (so to speak) to be the exponent. 



It would be difficult, I think, to find a more significant proof 

 of the value of the microscopic test than this result has'afforded; 

 and I venture to hope that, as I have spared neither time nor 

 trouble in the investigation, and am prepared to stake my 

 scientific character upon the accuracy of the observations now 

 detailed, they may not be lightly called in question. 



I should add, in conclusion, that, in addition to the foregoing, 

 I have examined chips of the shells of the following species of 



