i6o REPORT OF NEW JERSEY STATE MUSEUM. 



plane with valve, from which separated by very slight narrow 

 ridge. Spur about one-fourth of valve, lower end abruptly 

 truncated. Internally upper surface much roughened with finely 

 crenated ridges, and distinct crests for depressors cover whole 

 of so-called carinal prong. Compartments have radii and alse 

 with oblique summits, sometimes a little rounded, but not smooth. 

 Septa on sutural edges of radii remarkably fine, closely ap- 

 proximate, and denticuli excessively minute. Sutural edges of 

 alas most delicately crenated. Alse largely added to during 

 diametric growth of shell, and above level of opercular mem- 

 brane. Parietal pores square, rather large, crossed by trans- 

 verse septa almost close down to basis, and longitudinal septa 

 with tolerably large denticuli at bases. Pores in basis crossed 

 by numerous transverse septa. Basis sometimes irregularly cup- 

 formed in group-growing examples. 



Mouth with serrated labrum, teeth small and decrease in size 

 downwards on each side of central notch. Mandibles with third 

 tooth rather thick, blunt, and fourth and fifth knob-like. Maxillae 

 with inferior part projecting much beyond rest of edge, bears two 

 long single spines, between which and large upper pair in full- 

 sized example about seven pairs of moderately long spines, 

 feathered on their sides. Outer maxillse thickly clothed with 

 very fine spines and remarkably prominent. First cirrus with one 

 ramus with twenty-six segments, longer by ten segments than 

 shorter ramus, and both rami of second pair with segments re- 

 markably protuberant in front. Protuberance in upper segments 

 equals length of supporting part of each segment, and rami of 

 second cirri unequal in length by five segments. Third cirrus 

 with segments only slightly protuberant, rami considerably longer 

 than those of second cirrus, and no tuft of fine hairs at dorsal 

 base of pedicel. Sixth pair with upper segments elongated, bear- 

 ing six to seven pairs of spines, and dorsal spines short, thin, 

 few. Average full size about one-inch in basal diameter. 



(Darwin.) 



Remarks. — Known from the United States from about N. 

 Lat. 42° south to Charleston, the West Indies, Venezuela and 

 Honduras. It lives attached to floating wood, shells, bottoms 



