120 BULLETIN OF THE 



but most are waxen white ; shell inflated, beaks not very prominent ; epidermis 

 short except on the radiating lines, light brown, altogetlier rather sparse. Lon. 

 3.5 ; lat. 4.25 ; diam. 2.5 mm. Length of hinge line, 2.25 mm. 



Sigsbee, off Havana, 80 fms. 



The peculiarities of the hinge appear to be only specific characteristics, and 

 from Limatula through various forms of Limopsis to Glomus, Silicula, and Area 

 the hinge offers a series of easy transitions. The peculiar hinge, the " key- 

 stone " shape, the character of the tuberculation, and the small size, are the chief 

 characteristics of this little shell, which is perhaps alone in the group in show- 

 ing traces of bright coloration. 



Macrodon asperula n. s. 



Shell small, white, slightly inequivalve, excessively inequilateral, byssiferous ; 

 with a thin brownish epidermis radiatingly streaked with tliicker lines which 

 fray out into hairs, the whole being very fugacious ; hinge-line straight, the 

 area long and narrow, the beaks situated just within the anterior third of the 

 line ; ligamentary area extremely narrow, beginning under the beak, extending 

 close under the posterior areal carina obliquely to the posterior third of the 

 hinge-line, where k first reaches the margin, flat, black, with several white 

 longitudinal striae ; beaks well marked, not very prominent, with a faint de- 

 pression extending from them to the basal margin, marking the position of the 

 byssal gape ; outline like that of Philippi's Area aspera (Philippi, op. cit., II. 

 Tab. XV. ilg. 1 c), but much more inequilateral, the anterior end being smaller, 

 the posterior larger and more extended, and the line of the base much more 

 oblique, as would naturally follow from the above circumstances ; sculpture of 

 about- a do.^en (excluding those on the beaks) concentric sharp-edged subimbri- 

 cate ridges, being old margins of the shell as it were forming varices, fainter 

 and more close set on the beaks ; with strong rounded radiating riblets (near 

 the base al lOut four to a millimeter) continuous only from one varix to another ; 

 posterior part of the cardinal border somewhat aiiriculated or compressed, ante- 

 rior extreme rounded or moderately inflated, the anterior margin forming a little 

 less than a right angle with the hinge-line, the posterior a little more than a 

 right angle, the former slightly rounded to the base, where it is a little concavcly 

 excavated for the byssal gape, the latter first a little concave from the auricula- 

 tion, then very broadly rounded out and passing without any angle into the base ; 

 right valve a little the smaller ; interior white, both muscular scars double (by 

 the splitting of the ends of the adductors) ; margin smooth, sharp ; byssus slen- 

 der, tufted at the distal end, light brown ; hinge with six vertical teeth extending 

 from the position of the beaks anteriorly, the first four small, vertical, gradu- 

 ally enlarging forward, the fifth largest, and with tlie sixth somewhat ol)li(jue ; 

 hinge between the beak and the ligamentary furrow edentulous, bej'ond that 

 there are three horizontal teeth, the middle one largest extending posteriorly 

 nearly parallel to the hinge-line and to each other. Lou. 8.5 ; alt. 5.0; max. 

 diam. 3.25 ; lon. of hinge-line, G.25 mm. 



