304 L^LLETIN OF THE 



Myonera undata Verhili. 

 Necera undata Verrill, Trans. Conn. Acad. Sci., VI. pp. 223, 277, June, 1884. 



Habitat. Off Chesapeake Bay in 2221 fms. (Verrill); fragments were ob- 

 tained by the "Blake" in 450 fms. near Havana; at Station 175, near 

 Dominica, in 611 fms., ooze, bottom temperature 40®.0 F.; and at Station 230, 

 near St. Vincent, in 464 fms., bottom temperature 41°.5 F. 



This species must attain a considerable size and remain extremely fragile. 

 The pieces obtained by the " Blake " indicate its place to be with Myonera, 

 but there is no buttress or appearance of an internal rib. 



Myonera lamellifera Dall. 



Ne(Bra lamelUftra Dall, Bull. M. C. Z., IX. p. 113, 1881. 

 Plate III. Fls. 7. 



Habitat. Station 36, 84 fms. ; a single right valve. 



A comparison of figures will show that Mr. Smith's Necera consociata is 

 wholly distinct from this species. N. semutrigosa Jeffreys, is less oblique in 

 form, and the concentric rugae are mere threads, not rising clear and sharp 

 from the shell as in M. lamellifera. Moreover they belong to entirely different 

 groups, semistrigosa being a typical Cuspidaria. The present species has a faint 

 rib leading to an obsolete buttress, but no teeth, while the fossette lies poste- 

 riorly directed in a narrow groove on the hinge margin. 



Its nearest relative seems to be the next species. 



Myonera limatula Dall. 



NecBra limatula Dall, Bull. M. C. Z., IX. p. 112, 1881. 



Necera contractu Jeffreys, P. Z. S., 1881, p. 941, pi. Ixxi. fig. 4, 1882. 



Plate III. Fig. 5. 



Habitat. Station 44, 539 fms., off Tortugas; bottom temperature 39°.5 F. 

 Two perfect and two broken valves. 



None of the specimens of Necera contracta in the Jeffreys collection at 

 Washington show any tooth whatever in either valve. The posterior cardinal 

 margin of the right valve is bevelled off a little, to fit in under the edge of the 

 left valve, but it is not a tooth in any ordinary sense. 



It differs from the preceding species in its smaller size with equal length, 

 finer and less elevated sculpture, and less evident posterior ventral sulcus. In 

 one right valve there is a point extending forward and downward from under- 

 neath the middle posterior hinge-line, but this seems clearly pathological. 

 There is no buttress or rib internally. 



