Fossils of the Niagara and Clinton Groups. 59 



cliaracter may be either preserved or entirely lost. Although the general 

 and prevailing form is oval or ovate, yet we not unfrequently meet with 

 forms that are roundish, and the ventral valve wider than long." Figures 

 2 and 3 are examples of two of the shapes in which this species occurs. It 

 is very abundant in the Clinton group, and is also found in the Caradoa 

 formation in England. 



Pentamerus, Greek ; 5-partite, in allusion to the 5 chambers inside 

 of the shell of this genus. 



Ichthyocrimis laevis. — The encrinites of the genus Icthyocrinus have a 

 round slender smooth column, fire plates in the pelvis and five primary rays, 

 but no interradial plates as in Glyptocrinus. The rays are subdivided into 

 eecondaries, tertiaries, &c., at irregular intervals, and the free arms are com- 

 posed of single flat plates, like those of the cup below. It does not clearly 

 appear from the descriptions of this genus given by the different authors, 

 whether or not, the primary rays consist always of three plates. Professor 

 McCoy says three, but Professor Hall says that the first subdivision takes 

 place upon the fourth or fifth plate from the pelvis. This species is very 

 often found with its arms folded up over the summit. It is considered by 

 gome geologists to be identical with the / pyriformis of the Dudley Lime- 

 Btone in England. It certainly resembles it very much. Sir R. Murchison 

 says the English species " extends its range to North America," having 

 allusion, no doubt, to the one now under consideration. It is found in the 

 Niagara shale at Lockport, and will probably be discovered in Canada. — 

 The name appears to have been derived from Icthys, a fish ; and Krinos, a 

 lily ; LcBvis, smooth. 



Strophomena depressa,f[g 5, is a fossil of a genus closely allied to Lepte- 

 na. It has a straight hinge line, the surface of the shell is flat and furrowed by 

 strong concentric undulations, and the margin at the sides and base is abruptly 

 bent down. It is often the same breadth above as it is at the base, and it is 

 then of a square shape, with the two lower angles rounded. The surface is 

 also marked by radiating lines ; fig 5 is a specimen full grown, but they are 

 sometimes much smaller and not so broad above in proportion to their size. 

 This species is also known by the name of Lepiena depressa. 



The generic name Strophomena is derived from the Greek, strophos, 

 bent ; and mene, crescent, in allusion to the shape in Avhich one valve is 

 bent under the other. In the first reports of the New York Geologist, this 

 fossil is called Strophomena depressa. In the second volume of the 

 Palaeontology of New York, it is designated Lepiena depressa. In a 

 recent and beautifully illustrated memoir upon the Bracliiopoda of Great 

 Britain, by T. Davidson, Esquire, F. G. S., published in the works of the 

 Palgeontographical society of London, the genus Lepiena is divided, and 

 this species falls back into the section Strophomena, which will henceforth 

 most probably, include several other American fossils now classified in the 

 genus Lepiena. This fossil is also known as Lepiena or Strophomena 

 rhomboidalis. 



