Oi\ Some Xew Forms of Bkachiopoda. 245 



[Plate 13, figs. 4, 5]. It remains to l)e determined whether other species 

 described in the same paper * as Lingula really beloi;g to the same 

 genus. 



In that communication I proposed the generic name of Lingulepis 

 for the form described by Dr. Owen as Lingula pinnaformis. 



In ISGl Mr. l)illings proposed the name Obolella for some small 

 shells of the Lower Silurian rocks, and this genus will probably include 

 the species originally described by Mr. Conrad as Lingula jprimn . It 

 is not improbable that the shell known as Lingula antiqua may belong 

 to Le^gulepis. The foundation to our claim for recognizing the genus 

 Lingula in the lower sandstones is therefore very much M-eakened, to 

 say the least, and until shells demonstrated to be true Lingulie are 

 shown to occur in our Silurian rocks, I think that we have a right to 

 assert the contrary. Indeed, I am extremely doubtful whether we 

 have yet evidence to claim the occurrence of a single species of true 

 Lingula in the Lower Palaeozoic rocks. 



In a late examination of some Lower Silurian species, usually desig- 

 nated as Lingula, one of them was found to possess a muscular impres- 

 sion differing entirely from any described Linguloid species. The 

 ventral (?) valve presents a small area with a narrow pedicel groove, and 

 a large lobed muscular impression, which in the cast extends as a narrow 

 ffroove, toward the base of the shell. The character of the area and 

 foramen differ from the typical forms of Lingulella, though in that 

 genus the form and character of the muscular impression has not been 

 determined, so far as I am aware. For this shell I propose the name 

 LiNGULOPS. [Plate 13, figs. 1, 2.] 



We have, therefore, in our Lower Silurian rocks the genera, Lm- 

 GULELLA, Lingulepis, Obolella and Lingulops, which have heretofore 

 been referred to the genus Lingula, while the characters of this latter 

 genus have not yet been identified in any species of this Geological 

 period. 



There is still another Linguloid form, occurring both in the Lower 

 Silurian and Devonian, and probably in the Middle Silurian, having a 

 longitudinal septum in one or both valves, and which it will be conve- 

 nient to separate for the present under the name Dignomia [Plate 13, 

 fig. 3] ; and it is probable that still another type may be indicated. 

 The material, therefore, among which true Lingula is to be sought is 

 very much restricted. 



Adopting the generic name Okbiculoidea, it will embrace many of 

 our so called Discina, and, indeed, it may be questioned whether we 

 have any true Discina in the older rocks. The details of the charac- 

 ters of these genera will be discussed in another place. 



* Sixteenth Annual Report on the N. Y. State Cabinet of Natural History. 



