INVERTEBRATES. 323 



This group will, we think, almost beyond doubt, include two South Ameri- 

 can shells, described by d'Orbigny, from the Carboniferous rocks of Bolivia, 

 under the names Terebratula Andii and T. GaudreyL Indeed we have some 

 suspicions that his T. Andii may even be specifically identical with the type of 

 our group. D'Orbigny's figures appear to represent a more coarsely striated 

 shell than ours, and show the plications extended farther towards the beaks; 

 but Mr. Salter refers to that species, under the name Orthis Andii, a shell col- 

 lected by David Forbes in the Andes (Quart. Jour. Geol. Soc., xvii, p. 64, pi. 

 iv, fig. 3), that agrees almost exactly in form, as well as in the plications, with 

 that before us. It shows, however, no radiating striae, but they were probably 

 in part obliterated by wearing, for so careful an observer as Mr. Salter would 

 not refer a perfectly smooth shell, to as distinctly striated a species as d'Orbig- 

 ny 's figures represent. We also regard Choristites Lamarckii, of Fischer, = 

 Spirifer Lamarckii, Murchison, de Verneuil and Keyserling, (Geol. Russ , ii, 

 pi. vi., fig. 8a, 8 6], as most probably another example of this genus. The 

 distinguished authors of the Geology of Russia, were evidently in doubt in 

 regard to the affinities of the last mentioned species, of which they had no per- 

 fect specimens, and state that they would have referred it to Terebratula, had 

 it not been for the fact that Fischer described it as having a straight hinge, 

 and a triangular foramen. 



So far as we know, this genus is strictly confined to the Carboniferous rocks, 

 and includes but few species. It belongs to the Strophomenidse, near Orthis. 



We have not had access to Fischers's work, and consequently do not know 

 what characters he assigned to his proposed genus Choristites, nor what species 

 was regarded by him as its type. From the species included under that name 

 by him, however, it seems manifest he intended it for the same group for which 

 Sowerby's older name Spirifer, is now retained. We~also have the impression 

 that Spirifer mosquensis was his typical species of Choristites. Should it be 

 the fact, however, that the species Lamarchii was the type of his genus, and 

 that it has the internal characters of our genus, it would be necessary to retain 

 his name Choristites, for the group under consideration. If so, we shall have 

 no objection to abandoning our name, and calling the American species Choris- 

 tites hemiplicatus, for we shall always yield cheerfully to the law of priority. 



Syntrielasma hemiplicata, Hall (sp). 



Spirifer hemiplicatus, Hall, 1862. Stansbury's Report Great Salt Lake Exp., p. 409, 

 pi. iv., fig. 3a, 36. 



Shell in young examples, moderately convex, and resem- 

 bling a "resupinate" Orthis, in adult specimens often so gib- 



