72 On the Shell-structure of Spirifer cuspidatus &c. 
the singular correspondence between the patchy distribution of 
the perforations in Nos. 2,3, 4 and that which is characteristic 
of Syringothyris (No. 1)—a correspondence which is the more 
significant as I have not elsewhere encountered this peculiarity. 
On slicing 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, ¢r.) con- 
Fig. 3. Fig. 4. 
Fig. 3. Transverse section of Syringothyris from Millecent, from a drawing 
by Mr. Davidson: /,/, dental plates ; ¢r, transverse lamina; ¢, incom- 
plete tube. 
Fig. 4. Transverse section of true Spirifer cuspidatus from Millecent, from 
a drawing by Mr. Davidson: J, /, dental plates. 
necting the dental plates (/, 7), with its projecting pair of 
lamelle forming the nearly complete tube (¢) 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 imperforate 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 (4B), it proved that its dental laminee (1, J, 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 zsomorph of Spirifer cuspidatus, not distin- 
guishable from it by external conformation, but generically 
differentiated by a very marked peculiarity of internal structure, 
of which peculiarity the perforated 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 
