174 PERMIAN FOSSILS. 



though it might; with equal propriety, have been doubtingly referred to the present 

 species, it follows that I am quite disposed to extend its range to the Permian region 

 of Germany. 



Byssoarca Kingiana, Be Verneuil. Plate XV, figs. 10, 11, 12. 



Arca Kingiana, Be Verneuil. Bull. Soc. Geol. de France, 2°"' serie, vol. i, p. 32, 1844. 



— — ,, Geol. Russ., vol. i, p. 224 ; vol. ii, p. 313, pi. xix, fig. 11, 



1845. 

 Byssoarca Kingiana ,, King, Catalogue, p. 11, 1848. 



Arca — „ Howse, Trans. T. N. F. C, vol. i, p. 247, 1848. 



— — ,, Geinitz, Versteinerungen, p. 9, pi. iv, fig. 8 a, b, c, 1848. 



Diagnosis. — " Shell inequilateral, oval, transverse, twice as wide as it is long, and 

 truncated obliquely at its posterior extremity. Umbones projecting, situated near the 

 anterior extremity, which is round. Cardinal margin straight, terminated posteriorly 

 by an obtuse angle ; with a narrow, triangular, depressed area between the back and 

 the cardinal margin. The valves apparently smooth externall3^''^ (De Verneuil.) 



Byssoarca Kingiana, for the name of which I feel highly complimented by M. de 

 Verneuil, who first described it, is very distinct from the foregoing species, although, 

 in one respect, not to the extent implied by the original diagnosis ; since the valves, 

 instead of being smooth externally, as suspected by De Verneuil, are marked with 

 rather distant, slightly raised, occasionally dichotomous lines diverging from the 

 umbones : these lines might be considered as an incipient form of the ribs charac- 

 teristic of Byssoarca striata and B. tumida. It cannot, however, be confounded with 

 either species ; as its areas are much narrower, being, in fact, only slightly developed ; 

 its umbones more obtuse ; its dorsal slopes less impressed ; and its byssal sinuses 

 smaller. Besides, it does not appear to attain so large a size : my largest specimen is 

 an inch in width, and half an inch in length. 



This species is much scarcer than its associated congeners ; but it is more widely 

 diffused. I have found it only, and very seldom, at Tunstall Hill, in Shell-limestone. 

 Dr. Geinitz notices the single German locality, — Konitz, in Zechstein-dolomite. M. de 

 Verneuil discovered it in the Iltchegulova limestones, forming the base of the Permian 

 system, in the valley of the Dioma, government of Orenburg, Russia ; and Count 

 Keyserling records its occurrence on the Wymm, in Petschora-land. 



Family Nuculid^, King. 



The members of this group have hitherto been placed in ArcidcB ; but both their 

 shell and mollusk possess characters clearly diagnostic of a distinct family. Arcidoe 

 and Nuculida appear, in short, to be only approximately allied : it must not be over- 



^ Geology of Russia, vol. ii, p. 313. 



