BIVALVIA. 257 



but at Walton Naze, in the Red Crag, small specimens and fragments may be plenti- 

 fully obtained. 



The «ame proportional and other differences exist between this and the recent 

 British shell as between S. siliqua and S. gladiolus, and on that account I imagined it 

 to be specifically distinct when my ' Catalogue' was drawn up, and proposed for it the 

 name of S. ensiformis, from its near relationship ; but I now believe the Crag shell to 

 be entitled to no more, if scarcely so much, as a distinct variety, the form and position 

 of the muscular impression varying according to the greater elongation of the shell 

 being nearer the extremity in the more lengthened or attenuated varieties, this elonga- 

 tion probably being dependent upon some peculiarity of habit or locality. 



In some specimens given to me as Solen Americanus, the proportional length is even 

 greater than in the recent British shell, and with a rounded termination ; and none 

 of the specimens that I have seen from America appear entitled to a specific appellation 

 different from that of ensis. 



S. marginatum has, in the living state, a wide geographical range, being found on 

 the coast of Finmark [Loveri), and according to Von Hemprich is an inhabitant of the 

 Red Sea ; but I have never met with a fragment in any of the Crag Formations that 

 could be justly assigned to that species. 



S. {Ceratisolen) legumen is given by Mr. Smith in his ' List of Shells from the Clyde 

 Beds.' 



Cultellus,* Schumacher ; 1817. 



Cultellus. Desmoul. 1832. 



Solen (sp.) Spengler, Linn., Chemn. 



Generic Character. " Testa aquivalvis, transversim oblongd, subcomplanatd utrinque 

 Mans. Car do in valvd dextrd ; denies duo cardinales subcompressi alter erect us, alter 

 decumbens. In valvd sinistra cardinales ires medius sub-bijidus, apicibus divaricatis 

 anterior decumbens. In utraque valvd callus marginalis." — Schum. 



Type. Solen cultellus. Animal ? 



There is, I think, full justification for considering this as entitled to generic isola- 

 tion ; the very peculiar form of the hinge furniture, as well as the position of the 

 ligament (being removed to some distance from the extremity), are characters very 

 different from those of Solen. 



There are at present but few species known, either in a recent or fossil state, 

 possessing the above characters. Two or three shells, with this peculiar form of hinge, 

 have been obtained from the Older Tertiaries, but I am not acquainted with any of an 

 anterior date. 



* Etym. Cultellus, a little knife. 



34 



