794 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



internal posteriorly. Just beneath the beak is an elongated tooth-like 

 thickening of the inner margin which consequently curves downward 

 at this point. Muscular scars whitish, inconspicuous. The external 

 surface, so far as visible, seems to be smoothish with irregular lines of 

 growth. 



Length, 1.0 mm.; height, 1.4 mm. 



Two valves, station 949, N. lat. 40 3', W. long. 70 31', in 100 fathoms, 

 1881. This species is encrusted very much as Cryptodon (Axinulus) 

 ferruginosus, but is quite different in its much more strongly developed 

 hinge and ovate form. 



From station 2113, N. lat. 35 20' 30", W. long. 75 19', in 15 fathoms, 

 there are three specimens (No. 35531) of considerably larger size which 

 agree closely with this species and are probably identical. They are 

 more extensively encrusted with ferruginous mud and are somewhat 

 higher in proportion to their length; the ventral margin being slightly 

 produced in the middle, but they have the same posterior angulatiou 

 and the same evenly produced anterior end. The beaks are larger, 

 rounded, and relatively more prominent above the margin. The hinge- 

 margin is very thin and delicate, but does not differ essentially in other 

 respects from the smaller specimens. 



Length, 2.0 mm.; height, 2.2 mm. 



AXINOPSIS ORBICULATA G. O. Sars, variety INEQUALIS, new. 



(Plate XCII, figs. 5, 6.) 



Axinopsis oi-lnculaia G. O. SARS, Mollnsca Keg. Arctic.-e Norveghv, p. 63, pi. 19, 

 figs, lla-rf, 1878. VERRILL, Trans. Coim. Acad., V, p. 569, 1882. BUSH, 

 Proc. U. S. Nat. Mus., VI, p. 243, pi. ix, fig. 4, 1883. 



The numerous specimens of this species show considerable variation 

 in form and character of the hinge. Many specimens show the cardi- 

 nal tooth and pit as described and figured by G. O. Sars; others have 

 the hinge-margin nearly smooth or with mere rudiments of a tooth and 

 pit. Our specimens moreover show a thin, continuous external liga- 

 ment, which should be lacking according to Sars' description, but he may 

 have overlooked it. In form many of our specimens are evenly rounded, 

 as figured by Sars, but others have the antero-dorsal margin more con- 

 cave and the anterior end somewhat produced, while the postero- dorsal 

 margin is somewhat straighter than usual. 



Specimens from the Bay of Fundy have a somewhat oblong form, 

 with the ventral margin more nearly straight or but slightly convex, 

 and with the anterior end distinctly produced. This form seems suffi 

 ciently distinct to receive a varietal name, and we therefore propose to 

 call it variety inequalis. 



