NO. 1139. DEEP-WATER MOLLUSCA-VEREILL AND BUSH. 825 



LIMATULA HYALINA, new species. 



Shell small, thin, translucent, vertically ovate, somewhat oblique, 

 and produced postero-ventrally. Hinge- line straight, rather short, 

 forming a well-marked angle at each end owing to the outline of each 

 margin becoming somewhat concave below. Beaks small, acute, in- 

 curved. Umbos prominent, smooth, beyond which the shell is covered 

 with numerous, clearly defined, rather sharp radial ridges, separated 

 by wider concave intervals; from twenty to twenty-five of the radii can 

 be easily counted ; toward the posterior margin they become faint and 

 indistinct, while the extreme margin, on both sides, is smooth. The 

 anterior margin is broadly rounded and slopes backward below the 

 middle; the posterior margin is nearly straight or even a little incurved 

 in its upper half, but becomes slightly convex below; the ventral mar- 

 gin is evenly rounded and the edge is slightly scalloped by the radial 

 ribs and furrows. There is no distinct median sulcus or larger ribs. 

 The ligameutal area is rather short and broad with a relatively large 

 and thick central ligament which occupies a distinctly excavated pit in 

 the hinge-margin. 



Length of one of the largest specimens, 4.5 rnni. ; height, 7.5 mm. ; 

 thickness, 3 mm. 



A number of live specimens, among Forarniuifera, stations 2307 to 

 2374, N. lat. 29 +, W. long. 85 +, in 25 to 27 fathoms, 1885. 



This species somewhat resembles Limatula confnsa Smith, which was 

 also taken in the north Atlantic and West Indian areas, in 450 to 1,450 

 fathoms. Our species is, however, more compressed and more oblique, 

 and the radial ribs do not extend to the extreme margins as in the lat- 

 ter. The hinge-margin is also relatively shorter and the ligameutal 

 area larger, so that the beaks are more separated. 



Family PECTINID.E. 



In this family the classification adopted is that proposed by the 

 senior author in a recent paper on the group. 1 We give here a brief 

 abstract of the existing genera and subgenera therein described. For 

 fuller discussions of the characters and interrelations of these groups 

 and illustrations of typical species of most of them, reference should 

 be had to that article. 



In the following synopsis the generic groups are arranged in chrono- 

 logical order, without regard to their zoological affinities. 



1 "A study of the family Pcctinida-, with a revision of the Genera and Subgenera." 

 By A. E. Yen-ill, Trans. Coun. Acad. of Sciences, X, pp. 43-95 (six plates), July, 1897. 



