CLASSIFICATION OF THE BRACHIOPODA. 



95 



Obs. Having in Part HI, p. 65, entered fully into the history and reasons for adopting 

 the term Bhynchonella, in preference to other names subsequently proposed, I shall only 

 add that I cannot coincide in Professor M'Coy's views on the supposed distinctions 

 between this genus and that proposed by M. d'Orbigny, under the name of Hemithyris, 

 since from an attentive examination of the interior of both M. psittacea {Hemithyris, 

 D'Orb.) and R. octoplicata [Bhynchonella, D'Orb.), it will be easily perceived that both 

 were provided with similar dental plates, and, in fact, with every essential external and 

 internal character or detail of organisation ; nor has M. d'Orbigny proved that his so- 

 termed genus varied in any one important character. Professor M'Coy states that in 

 HemithyriSy " the foramen is triangular, and not separated from the hinge," nor is it so 

 in several admitted Mhynchonella {B. concinna, &c.), in which the foramen is partly com- 

 pleted by the umbo, the deltidial plates being lateral, and only rudimentary, as seen in 

 the recent B.psittacea and nigricans; in the Palaeozoic as well as Oolitic species we 

 find some forms in which the beak is so much incurved, as to exhibit no aperture or 

 passage for pedicle fibres, proving that the animal may have hved free during perhaps the 

 whole, or a portion of its existence. Professor M'Coy is also mistaken while stating, in his 

 ' Brit. Pal. Fossils,' that I refer Hemithyris to Hypotliyris of Phillips ; on the contrary, I 

 clearly stated that I saw at that period no good reasons for adopting either of these de- 

 nominations ; besides which. Professor M'Coy gives examples of Hemithyris, which do not 

 even possess the internal characters of his diagnosis. 



Geol. range. — The genus RhyncJionella is one of the oldest types of animal life, having been 

 repeated from the Silurian epoch up to the present period : two species are still found alive. 



Examples : B. acuta, Sow., sp. ; antidichotoma, Buv., sp. ; concinna. Sow., sp. ; Cuvieri, 

 D'Orb. ; decorata, Schl., sp. ; furcillata, Theodori, sp. ; plicatella. Sow., sp. ; octoplicata, 

 Sow., sp. ; plicatilis. Sow., sp. ; tetrahedra, Sow,, sp. ; psittacea, Chemnitz, sp. ; nigricans, 

 Sow., sp. ; Bouchardii, Dav. ; acuminata, Martin, sp. ■} pugnus, Martin, sp. ; lacunosa, 

 Lin., sp. ; Wilsoni, Sow., sp. ; spinosa, Schl., sp. ; &c. &c. 



^ In R. acuminata, the arms were attached to small curved lamellae, similar to those of all the 

 Rhynchonellae ; a beautiful example may be seen pig. 33. Fig. 34 



in the Museum of Practical Geology. I have 

 thought that it might be interesting to introduce 

 figures of two remarkable internal casts, on 

 which the muscular scars, ovarian spaces, and 

 vascular impressions are beautifully illustrated. 

 Fig. 33 is taken from a specimen belonging to 



Professor King: the view is drawn, as 



seen from the beaks, with the smaller 



or dorsal valve uppermost : a, adductor; 



R, cardinal muscles; 0, ovarian spaces ; 



V, vascular impressions. 

 Fig. 34 shows, in a beautiful manner, the impressions due to the vascular system in the dental or ventral 



valve, and has been drawn from a specimen in the collection of Mr. Morris. 



Rh. acuminata, Martin, sp. 



