930 PKLECYPODA. [Eulamellibranchia. 



the resilium, which is the most important character of the genus ; 

 they are nearly parallel to the edges of the valves, the anterior ones 

 more elongated than the posterior ones ; the dorsal lamella? are re- 

 curved at their upper extremity, forming a hook over the adjacent 

 lamella^ ; the lamella? of the right valve are more dorsal than those 

 of the left. Resilium internal, below the beaks, oblique. Adductor- 

 scars much impressed, the posterior nearer the apex. 



Diameter Ant. -post., 1 mm. ; dorso-ventral, 2 mm. (type). 



Type in the Mus. Hist. Nat,, Paris. 



Hab. Stewart Island, in 35 fathoms, type (Filhol) ; Foveaux 

 Strait, in 15 fathoms (A. Hamilton). 



Genus 7. ROCHEFORTIA, C. Velain, 1876. 



Rockefortia, Velain, " Comptes Rendus," 1876; Archive Zool. Experim., vi. 

 1876, 132. Type: E. australis, M.-Ch. & Vel. Montacuta (sp.), Tur- 

 ton, Dithyra Brit., 1822, 60. Anatina, Brown, 111. Conch. Great Brit., 

 1st eel., 1827. Tellitnya, Sect, ii (sp.), Brown, op. tit., 2nd ed., 1844. 

 107 ; H. and A. Adams, G.R.M., ii, 478. Mysella. Angas, P.Z.S., 1877, 

 176. 



Shell small, ovate or rounded quadrate, anterior end longer : 

 hinge with a short internal subumbonal resilium and traces of an 

 amphidetic, obsolete, external ligament ; on either side of the resilium 

 the cardinal margin bears a simple oblique lamina, the pair divari- 

 cating from the umbo and without any hook at the proximal ends ; 

 they are separated visually in one valve from the dorsal margin by a 

 groove parallel to it, and above this groove the margin in some cases 

 is thickened so as to form another lamina ; the single laminae of the 

 opposite valve, sometimes represented only by inflected and bevelled 

 extensions of the valve-margin, are received into the grooves above 

 the laminae of the first-mentioned valve, and the right anterior lamina 

 is longer than the right posterior one. From Bernard's researches 

 into the development of the hinge it is evident that these lamina? 

 represent the secondary lamina? of such forms as the Veneridce before 

 the latter break up into cardinal and lateral teeth properly so called ; 

 but in rare instances the laminse of the present group begin to show 

 signs of a tendency to separate, so that the distal portions are more 

 elevated than the medial part, and the former might be taken for 

 laterals and the proximal ends for obscure cardinals, which in a 

 genetic sense they really are. The ventral portion of the resilium 

 carries a calcareous coating which in well-developed specimens is 

 distinguishable as a lithodesma or " ossicle." (Ball.) 



The type is from the Island of St. Paul. 



Fossil in the Tertiary. 



KEY TO SPECIES. 



A. Shell quadrately cuneate, with very fine sharp concentric stria* donaciformis. 



B. Shell transversely ovate, with strong concentric riblets, re- 



ticulated by fine radiate threads . . . . . . reniformis. 



