210 REMARKS ON FOSSILS OF PERMO-CARBONIFEROUS AGE, 



Geuus CYRTINA, Davidson. 



Cyrtina CARBONARI a, McCoy, var. austral as ica, var. nov. 



Pentamerus carhonarius^ McCoy, Ann. Mag. Nat. Hist. 1852, 

 X. p. 426. 



Pentamerus carbonaritcs, McCoy, Brit. Pal. Foss, 1855, fas. 3, 

 p. 442, t. 3d, f. 12-18 



Cyrtina (?) carbonariits, Davidson, Mon. Brit. Garb. Brach. 

 1858, pt. 2, p. 71, 1. 15, f.5-14. 



Si?, char. — Shell elongately oval, longer than wide, constant in 

 shape, straight-sided, rough. Valves bi-convex, or in some cases 

 nearly plano-convex, the ventral valve being much arched. Hinge 

 shorter than the width of the shell. Ventral valve inflated, 

 very convex; beak strongly incurved, overhanging the area 

 which is concave, broad, and wide ] sinus well marked, 

 but narrow, and more or less angular ; fissure large. 

 Dorsal valve either nearly flat, or slightly convex ; mesial fold 

 low ; umbonal region flattened from abo\'e. In the interior the 

 septum of the ventral valve is more than two-thirds its entire 

 length. Surface of the ventral valve rugged, bearing a few (four 

 or five) thick, coarse, hardly radiate and prominent arched ribs, 

 but usually indistinctly sub-divided, or split, especially the pair 

 bounding the sinus, and all separated by angular interspaces ; 

 the bottom of the sinus occupied by a single rib. 



Ohs. — This truly British Carboniferous type is another important 

 form in the West Australian extinct fauna, and is exceedingly like 

 the shell found in the Northern Hemisphere, but possesses a greater 

 degree of regularity and less variation. It resembles the later 

 figures of Davidson, rather than the earlier ones of McCoy. 

 Although the genus has before been recorded from New South 

 Wales, I am not aware that this specific type has been met with. 

 The oval, almost egg-shaped outline, and coarse angular ribs give 

 the shell a very marked appearance. 



