NOTICE OF PALAEONTOLOGY OF NEW-YORK, VOLUME IV. IGl 



" mesial septum in the interior of the ventral valve supporting a small 

 " triangular chamber beneath the beak as in Pentamerus. In the dor- 

 " sal valve, no longitudinal septum, spires or loop; the whole of the 

 " internal solid organs consisting of two very short or rudimentary den- 

 " tal plates, which, in some species, bear prolonged calcified processes 

 " for the support of the cirrated arms. In all the species, the ventral 

 " valve has an area more or less developed. 



*'This genus includes three English species, which have been long known 

 under the names of Pentamerus lens^ P. liratus and P. Icpvis. AH these, 

 and the three Canadian species, abound in rocks of the age of the 

 Middle Silurian, such as the Llandovery rocks of Sir R. Murchison, 

 and the Clinton and Niagara groups of the New-York geologists. No 

 species have as yet been found either above or below the Middle Silu- 

 " rian. On the other hand, the Genus Pentamerus occurs more or less 

 frequently in all formations from the Black-river limestone to the 

 Devonian inclusive." 

 The European Pentamerus liratvs undoubtedly belongs to a genus dis- 

 tinct from P. knightii, having a straight hinge-line, an area on the ventral 

 valve, with a sensible mesial depression and corresponding elevation on the 

 opposite valve. The species has likewise a short septum, and supports a 

 small triangular pit in the ventral valve; while in the dorsal valve the 

 hinge-plate is divided, and the parts are extended in long lamellae into the 

 interior of the valve. The Pentamerus microcamerus^ M'Coy {=. Spirifera? 

 IcBvis, Sowerby), belongs also to the same group, having a straight hinge 

 and narrow area, with a short \/- shaped pit; characters unlike those of 

 true Pentamerus. At the same time, the Pentamerus lens and P.lcevis, 

 which, are, by Mr. Billings, united with P. liratus under the Grenus 

 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 \/- shaped pit is sup- 

 ported on a septum which sometimes extends for nearly half the length of 

 the valve. Moreover, the dorsal valve in the American species, P. oblongus, 

 is marked by the presence of very extended lamellae, which are united at 

 their origin and spread laterally till their free margins meet the correspon- 

 ding margins of the lamellae forming the X/- 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. oblongus and P. knightii or P. galeatus. 

 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. liratus and P. micro- 

 camerus among the European species, there is good ground for the separa- 

 tion ; but the other species do not appear to me congeneric. Through the 

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

 American species of Stricklandinia, S. gaspensis, S. ca7iadensis and 

 iS. a7iticostensis (Billings), and also the species referred to the European 

 P. lens. The first two appear to me to be congeneric with P. liratus, and 

 do possess the characters of the genus as described. Limiting, therefore, 

 the application of the term as here indicated, I think we have a well-marked 

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

 heretofore referred with doubt to Spirifera. I conceive, however, that 



21 Published March 1867. 



