NOTICE OF PALAEONTOLOGY OF NEW YORE. iQl 



fera? Icevis, Sowerbt), belongs also to tlie same group, liaving a straight 

 hinge and narrow area, with a short V-shaped pit ; characters unlike 

 those of true Pextamerds. At the same time the Pentamerus lens and 

 P. Icevis, which are, by Mr. Billings, united with P. Kratus under the 

 Genus Stricklandinia, appear to me to differ very widely from that 

 species. They have no area in the proper acceptation of that term, and 

 the hinge-line is not extended. In the ventral valve, the long V-shaped 

 pit is supported on a septum which sometimes extends for nearly half 

 the length of the valve. Moreover, the dorsal valve in the American 

 species, P. oUongus^ is marked by the presence of very extended lamellae, 

 which are united at their origin and spread laterally till their free margins 

 meet the corresponding margins of the lamellse forming the V-shaped pit 

 in the ventral valve ; and running parallel with it for nearly its entire 

 length, they then become vertical, and are continued as far as the middle 

 of the length of the valve, where their extremities apparently become 

 free. In these features, there is no essential difference between P. 

 ohlongus and P. knic/htii or P. geleatus. 



In Pentamerus lens, or a closely allied form, from Anticosti, the dorsal 

 valve possesses similar characters, and there is no area on the ventral valve. 

 Restricting the designation to such forms as P. liratiis and P. microccmiems 

 among the European species, there is good ground for the separation; 

 but the other species do not appear to me congeneric. Through the kind- 

 ness of Sir W. E. Logan, I have been permitted to examine the American 

 species of Stricklandinia, ;S'. gaspensis, S. canadensis and S. anticostemis 

 (Billings), and also the species referred to the European P. lens. The 

 first two appear to me to be congeneric with P. Kratus, and do possess 

 the chai'acters of the genus as described. Limiting, therefore, the appli- 

 cation of the term as here indicated, I think we have a well mai'ked 

 genus, which, typified by the species above named, may also include 

 others heretofore referred with doubt to Spirifera. I conceive, how- 

 ever, that our appreciation of generic limitations will not be enhanced 

 by including under the same term the P. lens and P. ohlongus = P. 

 kevis. 



Though at first restricting the genus to the Middle Silurian formations, 

 Mr. Billings has, at a later period, included under Stricklandinia the 

 Pentamerus elongatus of Vanuxem = Rensselceria ehngata (Hall), a Devo- 

 nian species. This form was first placed under Pentamerus, from its 

 resemblance to P. ohlongus; and I finally referred it to Renssel^ria, 

 from the generally similar shape, similar muscular impressions of the 



