92 [Senate 



GENUS PHOLIDOPS (Hall, 1859). 

 Pholidops : Palaeontology of New-York, Vol. iii, p. 498. 



Shell small, patelliform; apex anterior, subcentral, excentric or terminal. Surface 



marked by concentric lamcllas of growth, which are more expanded on the 



posterior side. Interior a shallow oval cavity, with a bilobed or horseshoe-shaped 



muscular impression; the margin flattened or slightly deflected, and entire. 



These fossils are not unlike, in form and general aspect, to Discin"A (Orbicula 



of authors); and I had originally thus referred a species in the Niagara group, 



under the name Orbicula squamiformis ( Pal. New-York, Vol. ii, p. 250j. It is 



only recently that we have ascertained that these, little scale-like fossils are really 



univalve, like Patella; since in numerous examples there is no evidence of any 



other valve, and the muscular imprint is unlike any of the brachiopods of the 



DisciNA or Crania forms. 



In some of the specimens from the Hamilton group, the casts are beautifully 

 preserved, and show the impression of the muscular callosity in a good degree of 

 perfection. We have now four well-defined species of the genus, each one holding 

 a different geological position, viz: Pholidops squamiformis, of the Niagara group; 

 P. ovatus, of the Lower Helderberg group; P. terminalis, of the Oriskany sand- 

 stone; and P. hamiltoni(B, of the Hamilton group. The species are therefore of 

 Silurian and Devonian age, and will probably be found in the Carboniferous strata. 



PHOLIDOPS HAMILTONI^ ( n. s.). 



Shell ovate, broader near the anterior end; apex excentric, little elevated and 

 slightly inclining forwards, thin and flattened towards the margins. Surface 

 marked by fine closely arranged lamellose striae. Interior smooth, except an 

 ovate somewhat bilobed prominence beneath the apex, which marks the muscu- 

 lar impression. 



The casts of the interior show very distinctly a double indentation at the apex. 

 The surface, when magnified, shows some indications of minute interrupted ra- 

 diating striae. It is the smallest of the species described, having a length of fourteen 

 hundredths of an inch, and a width of twelve hundredths in the widest part. 



Geological formation and locality. In the shales of the Hamilton group, from 

 the shores of Lake Erie to the Genesee river. 



LEPERDITA PUNCTULIFERA ( n.s.)- 



Test minute, subcylindrical; the two extremities subequal, rounded; a scarcely 

 elevated point or tubercle near one extremity: the ventral margin of one valve 

 distinctly overlapping the other, and rising in a distinct ridge along the border. 

 Surface marked by minute puncta or pits, which are much more distinct and 

 regular than usual in the species of this genus. 

 Geological formation and locality. In shales of the Hamilton group, often very 



abundant on the shaly laminae ; from the shores of Lake Erie, to Canandaigua lake. 



The following figures will serve to illustrate more fully the characters described 

 in the observations upon the Genera Athyris, Merista, Meristella. and Leio- 



EHTNCHUS. 



