7S"4 PROCEEDINGS OF THE NATIONAL MTSKUM. VOL.XX. 



This genus appears to be closely allied to Monlnciitu, but differs in 

 not having a definite, raised, posterior tooth; in having a large, elon- 

 gated posterior cartilage, bearing a large ossicle attached to a special 

 groove jilong a tooth-like ridge; and in having the structure of the 

 hinge in both valves nearly the same. In the position of the resiliuni 

 it resembles Erycina, but the latter has two large teeth in both valves. 



KELLIOPSIS ELEVATA (Stimpson). 



( Plates XCIII, figs. 2-4; XCIV, figs. 7, 8.) 



Montucutit bldentata GOULD, Rep. on Invert, of Mass., 1st ed., p. 59, 1841. (Not 



of .Montagu.) 



Montacuta elerata .STIMPSON, Shells of New Eng., p. 16, 1851. 

 Cyo in in in elfvatinn H. and A. ADAMS, Genera Recent Moll., II, p. 477, 1858. 

 Aloiitai-iita clcrtda Goi'LD, Rep. on Invert, of Mass., Binney's ed., p. 86, fig. 396, 



1870. TRYON, Amer. Mar. Couch., p. 172, pi. xxxm, fig. 440, 1873. VERRILL, 



Report Invert. Anini. of Vineyard Sd., iu 1st Rep. U. S. Fish Com., pp. 394, 



688, 1874 (anth. cop., p. 418). 

 Tellimya elerata DALL, Bull. U. S. Nat. Mus., No. 37, p. 50, pi. LXVIII, fig. 6 i.-is 



Montacuta elevata Stiuipson), 1889. 



This rare species has been obtained at low-water mark, at Savin 

 Rock, near ]S'ew Haven, Connecticut (J. E. Todd), 1871; Wellfleet, 

 .Massachusetts (Webster), 1879; Woods Hole, Massachusetts (Gut of 

 Canso), 1882; Naushon Island (Gutters and Sheep Pen Cove), 1882; 

 and Narragansett Bay, in Si to 10 fathoms, 1880. 



Family DIPLODONTID^J. 



UngulinidcK FISCHER; Diplodonticlte -f- Cryptodontida Dall. 

 CRYPTODON Turton, 1822. 



Type. Cryptodon flexuosus (Montagu). 



The typical species of this genus have no distinct teeth in either valve, 

 but the inner margin of the hinge-plate is more or less thickened or 

 swollen in front of and behind the beaks. The ligament is posterior and 

 lies in a long, curved furrow in the midst of the marginal thickening; 

 where it commences at the beak it is marginal and external, but as it 

 runs backward it recedes from the edge and becomes more or less 

 internal and invisible from the exterior. Moreover, the posterior end 

 of the shell has one or more distinct radial corrugations or plications 

 to give the thin shell strength enough to resist the action of the large 

 posterior adductor muscle which is attached directly upon the princi- 

 pal plication. The pedal muscle is attached to the upper plication 

 when the latter is present. Many writers have adopted the name of 

 Axlnus Sowerby, 1823, for this genus; the latter name was given to a 

 tertiary species, the structure of which is not fully determined. It may 

 belong to a very distinct genus. Moreover, Turtou's name seems to 

 have actual priority of publication. 



