238 Dr. Gwyu Jeffreys on Arctic 



These remarks, although critical, chiefly relate to the selec- 

 tion or adoption of specific names, and do not affect the value 

 of his excellent paper. Such difference of opinion among 

 zoologists as to the limits as well as names of species is not 

 only notorious, but useful. We are all actuated by the same 

 motive, viz. the honest and careful investigation of those 

 branches of natural histoiy to which we devote our attention ; 

 and I can truly give Mr. Smith the fullest credit for the 

 ability and zeal which characterize his work. . 



Modiolaria dtscors, Linne ; var. Icevigata. 



Modiola Icevigata, Gray in Suppl. to App. of Pany's Voyage, p. ccliv 

 (1824). 



At least half a dozen species might be made out of the 

 varieties of M. discors, if we regard size, shape, and the com- 

 parative number or absence of radiating strise as specific cha- 

 racters. I have examined many hundred specimens from 

 different places, and can scarcely find two precisely alike. 



Leda arctica, Gray. 



Nucula arctica, Gray, I. c. p. ccli. 



Mr. Smith has followed Broderip and Sowerby in referring 

 this to the species known as N. limatulaoi Say (1831), which 

 is probably N. lanceoJata of J. Sowerby (1817). But I must 

 adhere to my former opinion that Gray's species is the same 

 as the N. truncata of Brown (1827) . Gray gives the " length 

 (from front to back) half an inch ; depth (from umbones to 

 the opposite edge) a quarter;" he describes his shell as "very 

 slightly concentrically wrinkled " and " obliquely truncated 

 behind," all of which characters suit Brown's species. Leda 

 limatula is three times as long and deep, according to Gray's 

 mode of admeasurement ; it is not " concentrically wrinkled," 

 nor " truncated behind." As to Gray's shell being placed in 

 his division " behind slightly produced, gaping," his N. ros- 

 trata {L. pernula) is placed in another division, "behind much 

 produced, gaping." All these three species of Leda " gape " 

 more or less at the hinder extremity. Torell, in his admira- 

 ble treatise on the Mollusca of Spitzbergen, has fully demon- 

 strated that Gray's N. arctica is identical with Bro^vli's N. 

 truncata. Each of the above specific names has several 

 aliases. 



Saxicava rugosa, Linne. 



I prefer retaining this specific name for the following 

 reasons. We find, in the 12th edition of the ' Systema 



