BIVALVIA. 257 
but at Walton Naze, in the Red Crag, small specimens and fragments may be plenti- 
fully obtained. 
The same proportional and other differences exist between this and the recent 
British shell as between S. sé/iqua 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. exsiformis, 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 exsis. 
S. marginatus has, in the living state, a wide geographical range, being found on 
the coast of Finmark (Zovéz), and according to Von Hemprich is an mhabitant 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,* Schumacker, 1817. 
CuLTELLUS. Desmoul. 1832. 
SoLEN (sp.) Spengler, Linn., Chemn. 
Generic Character. “ Testéd equivalvis, transversim oblonga, subcomplanata utrinque 
hians. Cardo in valvd dextré; dentes duo cardinales subcompressi alter erectus, alter 
decumbens. In valvé sinistré cardinales tres medius sub-bifidus, 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 So/en. 
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 
