NO.H39. i>i-:i-:r-ir.iTKi; MOLLUSCAri:i;i:u.i, AND r.rsii. 841 



covered with small, close, radial ribs and crowded concentric ridges; 

 posterior auricle much smaller, with from one to three faint, radial 

 ridges and many concentric, raised lines, and with its outer end form- 

 ing less than a right angle, with a slight incurved notch below. In 

 the right valve the anterior auricle has a similar radial sculpture and 

 the byssal notch is rather deep and narrow. The dorsal lines of the 

 body of the shell form rather less than a right angle; the ventral mar- 

 gin forms nearly a semicircle with an obtuse angle where it meets the 

 dorsal outline. limbos a little prominent; beaks small, acute, smooth, 

 and projecting beyond the margin of the hinge. The surface of the 

 left valve is covered with slightly raised concentric lines, which are 

 interrupted or broken up by small arched scales which are sometimes 

 semicircular, but more frequently somewhat angulated or V-shaped, 

 and usually are separated by intervals about equal to their breadth; 

 these scales vary in number, but are usually arranged in about forty 

 radial rows, and increase regularly in si/e from the umbos, where they 

 are replaced by thin, slightly raised, radial lines crossing the stronger, 

 more elevated, concentric lines, but not rising into points. In some 

 specimens the radial arrangement is scarcely discernible; the scales 

 appear as irregularities in the concentric lines. The postero dorsal 

 area below the auricle is nearly smooth, except for the line lines of 

 growth, but sometimes shows minute granules. The right valve, which 

 is smaller than the left, is covered by fine, thin, close, concentric, 

 raised lines, which sometimes show microscopic striations. The ante- 

 rior auricle is decussated by from six to eight, or more, small radial 

 ridges, which are crossed by the raised, concentric lines; the latter rise 

 into sharp scales at the dorsal margin; the small posterior auricle has 

 finer concentric lines and only two or three faint, radial ridges. 



Comparatively few specimens, at three stations, between X. lat. 42 

 45' 30", W: long. G2 4r, and X. lat. 39 53' 30", W. long. 71 13' 30", 

 in 121 to 312 fathoms, 1877-1885. 



C. Icermadecensis (Smith), from north of Kermadec Islands, in GOO 

 fathoms, is a related species. 



PROPEAMUSIUM THALASSINUM (Ball) Verrill. 

 (Platt- LXXXVII, fig. 6.) 



Amusaium fenestratum VERRILL, Trans. Conn. Acad., V, p. 582, 1882. 



.ImiiKshim sp. VEUKILL, Trans. Com. Acad., VI, pp. 261, 281, 1884. 



1'i'cten ( Pseudamusium) tliala^sinus DALL, Bull. Mus. Comp. Zool., XII. p. 221. 1886; 



Bull. U. S. Nat. Mns., No. 37. p. 34, 1889. 

 I'ntpeamnsinm thalassintim VERRILL, Trans. Conn. Acad., X, pp. 87, !>L'. pi. xix, 



figs. 5-7, 1897. 



Found at thirteen stations, between X. lat. 40 5' 39", W. long. 70 

 23' 52", and X. lat, 35 42', W. long. 74 54' 30", in 43 to 317 fathoms, 

 1880-1885. South to Barbados, in 22 to 317 fathoms. Dall. 



