Mr. E. A. Smith on the Genus Splienia. 277 



XLIX. — Observations on the Genus Sphenia,7/>e7/« Descriptions 

 of new Species. Bj Edgar A. Smith. 



[Plate XV. A.] 



The genus Sphenia was originally founded by Turton * in 

 1822 for the well-known S. Binghami. It was founded on 

 conchological grounds only, and it was not until 1853 f that 

 an account of the soft parts was published. The genus has 

 relationship, either as regards the shell or the animal, with 

 Mya and Corhula ; indeed it is considered synonymous with 

 the former by Jeffreys |. On tlie other hand, M. Petit § 

 upholds its validity, observing that it differs from Mya by its 

 tliin shell, which is less gaping behind and very inequivalve. 

 The animal has relatively short siphons, and, at the base of 

 the foot, a true byssus. The Sphenias live attached in holes 

 in rocks, whilst tlie Myje rest buried in the sands. 



Mr. Clark j!, although admitting the geims, appears to Iiave 

 found very slender reasons for so doing. He observes : — 

 "This animal has great affinity to Saxicava, besides alliances 

 with Corhula and Mya\ indeed, the genus Sphcenia is almost 

 unnecessary, and its animal is nearly identical with Saxicava 

 arctica, and tlie structure of the hinge and the other hard 

 parts have much the same generalities." 



Sphenia is admitted as a distinct genus by Forbes and 

 Hanley, Tryon, Fischer, H. and A. Adams, and others. It 

 is united with illya by Jeffreys, and considered as a subgenus 

 of Corhula by Philippi and Woodward. 



After careful consideration I am inclined to agree to the 

 separation of this genus. Besides the differences between it 

 and Mya ])ointed out by M. Petit it is worth noting tiiat all 

 the species at present known are very small in comparison 

 Avitli the Mya'. 



M. Petit refers to the presence of a byssus as a distin- 

 guishing character ; but 1 would point out that J/^a in the 

 young stage also secretes that appendage ^[. 



Corhula dees not form a byssus, and, judging from the 

 C. yihha^ the sijjhons appear to be shorter than in Sphenia ; 

 also, like Mya, it lives buried in sand or mud, not in holes in 

 rock like Sjjhenia. 



* Couch. Ins. Jii'it. p. .'5(5. 



t Forbes and Iliuiluy, J'.iit. Mull. i. j,p. ItO-l');;. 



I ]>rit. Conch, iii. pp. (JO and 70. 



§ Cat. niuH. test. Kuroj). Lscl), ]^. -J-i-',. 



II J'.iit. Mariue Tost. Uo]l. (iH'w), p. 150, 

 ^! Jtli'ru}s, Urit. Conch, vol. iii. ]>. (JU. 



