190 REPORT ON THE STATE CABINET. 



labors of the European palaeontologists de Verneuil, Kixg, Barrande, 

 M'CoY, SuESS, Davidson, Salter and others. In the meantime, however, 

 other species have been referred to the genus, which, having the general 

 external characteristics of Pentamerus, still possess features that render 

 their union with that genus incompatible ; and farther study has shown 

 the necessity of separating them. Among the European forms which 

 are regarded as strictly referable to the genus, are P. knightii (Sow.), P. 

 vogulicus (de Ver.), P. galeatus (Dalm.), P. sieberi (Von Buck), P.jwlagicus 

 (Bar.), and P. ojjtatus (Bar.); while P. oUongus and P. lens have the 

 characteristic features of the genus less conspicuous, the exterior being- 

 smooth and the form less rotund. Pentamerus liratiis and P. microcamerus 

 have a straight hinge-line and distinct area. 



In 1859, Mr. Billings proposed the separation of certain forms from the 

 typical Pentamerus, under the name of Stricklandia (Stricklandinia*), 

 which he describes as follows : 



Generic characters. Shell usually large, elongate, oval, transversely oval 



or circular, sometimes compressed : valves nearly equal ; a short mesial septum 



in the interior of the ventral valve supporting a small triangular chamber 



beneath the beak as in Pentasibrus. In the dorsal valve, no longitudinal 



septum, spires or loop; the whole of the internal solid organs consisting of two 



very short or rudimentary dental 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 Pentame'rus lens, P. liratus and P. Icevis. All these, and 

 the three Canadian species, abound in rocks of the age of the Middle Silurian, 

 such as the Llandovery rocks of Sir E. Mdechison, and the Clinton and Niagara 

 o-roups of the New York geologists. No species have as yet been found either 

 above or below the Middle Silurian. On the other hand, the Genus Penta- 

 merus occurs more or less frequently in all formations from the Black river 

 limestone to the Devonian inclusive. 



The European Pentamerus liratus 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'Cor ( = Spiri- 



* In consequence of the name being preoccupied in botany, Mr. Billings bas proposed to change 



to STRICKLA^fDINIA. 



