CONTRIBUTIONS TO PALAEONTOLOGY. • 183 



CRANIA CRENISTRIATA (n.s.). 



Ventral or upper valve very depressed conical, subcircular in outline; apex cen- 

 tral or subcentral, a little inclined. Surface marked by sharp elevated crenulate 

 striae reaching almost to the apex (which is quite smooth), and increasing by 

 interstitial additions. 

 This species is quite rare, and two specimens only of the ventral valve are known 



at this time. The sharp elevated striae give the fossil, when partially obscured by 



adhering shale, the appearance of the exterior of the small funnelshaped fronds of 



Fenestella. 



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



county, N.York. 



CRANIA LEONI(n.s.). 



Shell subcircular, transverse or slightly elongate. Dorsal valve convex : ventral 

 valve concave, variable in form. The shell, towards the margin, is more abruptly 

 recurved : hinge-line straight, equal to a little more than one-third the width of 

 the shell. Muscular impressions of the posterior adductors in the dorsal valve 

 near the cardinal angles; the anterior ones near together and a little behind the 

 centre, with two minute impressions a little anterior to the centre, marking the 

 place of the retractor muscles. Ventral valve with the posterior adductors cor- 

 responding to those of the dorsal valve; the anterior adductors occupyijig a 

 subcircular area, and barely separated by an elevation marking the place of the 

 protractor muscle. 

 This species is known only in the condition of casts of the interior. The dorsal 



side is moderately convex ; the apex apparently a little excentric on the posterior 



side. 



Geological formation and locality. In the Chemung group : Leon, Cattaraugus 



county, N.York. 



ORTHIS LEPIDUS (n.s.). 



Shell small, transversely subelliptical, somewhat ventricose ; cardinal line little 

 less than the greatest width of the shell; area proportionally large; beaks di- 

 stant. Ventral valve very convex, regularly curved from beak to base : beak 

 prominent, pointed, slightly incurved. Dorsal valve depressed convex, marked 

 by a distinct mesial depression, which, in some specimens, extends nearly to the 

 beak : beak small, pointed, and but little incurved. Surface marked by fine ra- 

 diating striae, crossed by concentric striae and a few lines of growth- 

 This is the smallest species of Orthis yet known in the Hamilton rock, of this 



country, and is easily characterized by the great transverse diameter, the pr'^por- 



tionally large area, the prominent beak of the ventral valve, and the distinct jinus 



of the dorsal valve. 



Geological formation and locality. In shales of the Hamilton group : Ontario 



county, N.York. 



ORTHIS CYCLAS (n.s.). 



Shell small, varying from subcircular to transversely subelliptical, moderately 

 convex : beaks appressed, not distant; cardinal line rather less than one-half 

 the greatest width of the shell. Ventral valve convex, most gibbous near the 

 umbo : beak small, slightly incurved; area rather low. Dorsal valve the less 

 convex, sometimes marked by a shallow depression : beak very small, slightly 

 projecting beyond the cardinaj line; area small. Surface marked by strqng sharp 



