42 JOURNAL OF CONCHOLOGY. 



ON THE DISTINCTNESS OF 



THE GENERA TURTONIA AND CYAMIUM. 



By EDGAR A. SMITH, F.Z.S. 



Zoological Department, British Museum. 



The genus Cyamium was proposed by Philippi for a small shell 



which was collected by his brother at Gregory Bay, Patagonia. 



The animal or soft parts are unknown. Philippi's description 



runs thus : 



' Tesia transversa^ subincRquilatera, equwalvis, tenuis, vix hians ; 

 dejites cardinales in utraque valva duo, denies laterales 

 nulli ; liganientiim duplex, internum in foveola triangulari 

 pone denies cardinales ; impressiones musculares dues, ; sinus 

 palliaris nulbis.' — [Wiegmann's Archiv. Naturgesch., 1845, 

 P- 50]- 



The name Turtonia appears to have been first cited by 

 Alder in his ' Catalogue of the Mollusca of Northumberland 

 and Durham,' * where he refers to it the Venus niinufa of 

 Fabricius. The genus was however properly described by 

 Forbes and Hanley thus : 



' Shell minute, fragile, equivalve, very inequilateral, closed at 

 both ends, transversely oblong ; surface concentrically 

 striated or nearly smooth. Ligament external ; hinge with 

 two adjacent teeth in front, the anterior one laminar. 

 Pallial sinus simple.' — [Brit. Moll. vol. ii. p. 80]. 



On comparing these two descriptions it will be noticed 

 that the principal distinction consists in the ligament in the one 

 case being double, that is, partly internal and partly external, 

 and in the other external only. 



Notwithstanding Philippi's statement that his genus pos- 

 sessed an internal ligament, Jeffreys! unites with it the little 

 Turtonia minuta, which certainly has no internal cartilage. 

 He says that the type of Cyamium is a small shell from the 

 Falkland Isles (C. antarcticuni) and that he had several times 

 examined a series of specimens of that species in the British 



* Trans. Tyneside Nat. Field Club, vol. i. (1848), p. 189. 

 t Brit. Conch., vol. ii. p. 257. 



J.C, v., April, 1886. 



