242 PALEONTOLOGY OF NEW YORK. 



(3) 1879. Pentamerus, Bakkandb. SystSme Sihnien, vol. v, pis. xx, xxi, xxiii, Ixxvii, Ixxviii, Ixix, 

 cxvi, cxvii, cxviii, cxix. 



Pentamtnis, Hall. Eleventh Ann. Rept. State Geologist Indiana, p. 299, pi. xxvii, tig. 15. 



Peiitamerus, Whitfield. Geology of Wisconsin, vol. iv, p. 291, pi. xvii, figs. 11-13. 



Pentameriis, Davidson. Biitisii Silurian Brachiopoda, Suppl., p. 164, pi. ix, figs. 25, a. 



Gypidula, Walcott. Monogr. U. S. Geol. Survey, vol. viii, p. 159-161, pi. iii, figs. 4, 7; 

 pi. xiv, fig. 15 ; pi. XV, fig. 5. 



AntirhyncJionella, Q5hlert. Fischer's Manuel de Conchyliologie, p. 1311. 



SiehereUa, (Ehlert. Fischer's Manuel de Conchyliologie, j). 1311. 

 (1) 1889. Pentamerus, Nbttblhoth. Kentucky Fossil Shells, p. 1)4, pi. xxiii, figs. 12-14. 



(3) 1889. Pentamerus, Neitelroth. Kentucky Fossil Shells, jip. 59, 63, pi. xxvii, figs. 25-27; 



pi. xxxiii, figs. 25-29, 31-33. 

 (1) 1892. Pentamerus, R. Etheridge, Jr. Pentameridae of New South Wales; Records Geol. Survey 

 N. S. W., vol. iii, pt. 3, p. 52, pi. xi, figs. 5-9. 



(4) 1892. Pentainerus, Whiteaves. Contributions to Canadian Palaeontology, vol. i, p. 290. 



The elongate, subequally biconvex pentameroids being restricted to the 

 divisions above discussed, there remains to be considered the large group of 

 galeatiform shells which are characterized by their usually small size, inequal 

 convexity, and deep, overarching pedicle-valve. A typical representative of 

 this variable and undoubtedly heterogeneous group is the well-known 

 Atrypa {Pentamerus) galeata, Dalman. These are the fossils embraced in 

 UE Verneuil's grouping as " Pentamerus avec sinus," all having a median sinus 

 more or less strongly developed. Two divisions of the first order may be based 

 upon the position of this sinus, namely, those having it (1) on the pedicle-valve, 

 and (2) on the brachial valve. In the former division belong such species as 

 P. fornicatus, Hall, and P. Areyi, sp. nov., of the Clinton group; P. linguifer, Sow- 

 erby, and P. ventricosus, Hall, of the later Silurian, as well as shells which have 

 been referred to the Devonian subgenus, Pentamerella {P. arata, Conrad, P. dubia, 

 Hall, etc.). With the latter division we may place P. galeatus, Dalman, P. nuc- 

 leus, P. pseudogaleatus, Hall, P. (Sieberella) Sieberi, von Buch, etc , of the Silurian, 

 and the various species of the subgenus Gypidula (G. comis, Owen, G. l(zviuscula, 

 Hall, G. Romingeri, sp. nov.). This grouping might form a very convenient 

 arrangement of these species, were the field clear of generic terms, but in each 

 group designations of unequal value have been introduced, based upon varia- 

 tions in other respects than contour alone. The Devonian members of each 

 group develop with more or less distinctness a striated cardinal area and small 

 and convex deltidial plates, with some accompanying variation in the character 



