On Some New Forms of Brachiopoda. 247 



This fossil is certainly closely related to Obolus, while it preserves 

 certain characters which ally it with Trimerella. I am convinced, 

 however, of the necessity of proposing a distinct name for this form 

 in order that its relations may be more critically discussed. I would, 

 therefore, suggest the generic name Dinobolus. The relations of this 

 genus to Obolus are shown in the figures given (ut cit.). The exten- 

 sion of the median septum with the elevated lateral plates (the margins 

 of which, however, remain free below the muscular impression) are 

 features so similar to the same parts of Tresierella as not to escape 

 tlie most cursory comparison. In the latter genus, the lateral margins 

 of this elevated plate are recurved and conjoined with the inner surface 

 of the shell, leaving two tubular cavities beneath, separated by the 

 longitudinal septum. In Dinobolus the transverse plate below the mus- 

 cular imprints is rapidly narrowed to the median septum, leaving 

 beneath it on each side, a shallow cavity, the filling of which is shown 

 in the casts figured. 



The genus Trimerella will, therefore, at present, rest upon the 

 specimens figured by Mr. Billings, which possess the remarkable char- 

 acters indicated. Through the kindness of Mr. Selwyn, Director of 

 the Geological Survey of Canada, I have lately had an opportunity of 

 seeing the original specimens. A mold, made from the cast, showing 

 the extension of the plate on each side, and continued to the depth 

 indicated by probing beneath the processes, or filling of the cavities, 

 gives a form so similar to that figured by Dr. Lindstrom, as to leave 

 no doubt of the generic identity of the fossils. In the Canadian speci- 

 mens, the rostral portion of the cast is so much worn that the interior 

 character of the shell in that part cannot be determined, and therefore 

 we have not the means of comparing with the figure cited above. 



Among my collections made many years since at Gait, in Canada 

 West (Ontario), there is a cast of a ventral valve which bears some 

 resemblance to the casts of Trimerella. It has, however, a thickened 

 area or solid rostral extension with a central pedicel groove. The evi- 

 dence of median septum and transverse plates is obscure, and confined 

 to the central portion of the valve below the middle of its length, pre- 

 senting in the cast only the appearance of a strong duplicate muscular 

 impression, not unlike Obolus. For this [Plate 13, fig. 10] and allied 

 forms the name Rhynobolus may be adopted. The Oholus galtensis 

 Billings, will probably fall under this genus. 



[The above was originally intended as preliminary to a more extended 

 paper giving the results of examinations among the forms proposed as 

 new genera, but the author, having learned that similar investigations 

 with more extensive material were in progress by Mr. Davidson and 

 Prof. King, he has therefore deferred farther publication until their 

 work shall be completed. At the time of this writing (December, 1872), 

 they have already published a preliminary notice, entitled " Remarks 

 on the genera Trimerella, Dinobolus and JVIonomorella.] 



