Silurian and Devonian Fossils of Canada. 431 



Cystiphyllun sulcatum )Billings.) 



Description. — Short, turbinate, much curved, expanding at the 

 rate of between forty and forty-five degrees from the minute sharp 

 curved point upwards ; cup oblique, the lower margin being on 

 the side of the lesser curvature, moderately deep and nearly re- 

 gularly concave, the bottom covered with obscure course roun- 

 ded radiating ridges ; a shallow rounded groove or fossette exten- 

 ding from the centre to the higher margin, and in some specimens 

 two others much less distinct radiating to the sides at right angles 

 to the main groove. Exterior encircled by obscure undulations, 

 and longitudinally striated by the rudimentary radiating septa, 

 The vesicular structure consists of irregular sub-lenticular cells 

 from half a line to two lines in width ; length of the convex side 

 from one inch and a half to three inches, the usual length appears 

 to be about two inches or a little more ; width of cup from one 

 inch to one inch and a half; depth about half an inch. 



This species when the interior cannot be seen might be mis- 

 taken upon a superficial examination for a small curved Cyatho- 

 phyllum or Zaphrentis. It is about the size and shape of the 

 curved specimens of Petraia cornicula. 



Locality and Formation. — Rather common in the Corniferous 

 or Onondaga limestone on Rama's farm, Port Colborne. 



Collector — E. Billings. 



Genus Cyrtodonta (Billings). 



Generic Characters. — Equivalve, inequilateral ; umbones near 

 the anterior end ; general form obliquely tumid, transversely sub- 

 rhomboidal or ovate, posterior extremity larger than the anterior 

 and usually broadly rounded ; two muscular impressions, of which 

 the posterior is superficial and the anterior sometimes deeply ex- 

 cavated ; three oblique often more or less curved, anterior teeth, 

 situated either beneath or a little in front of the umbones ; two 

 or three remote posterior lateral teelh parallel with the hinge line ; 

 pallial line simple ; ligament external ; some of the species have 

 a narrow area between or behind the beaks. 



