LITHOTRYA CAUTA. 357 



with no distinct pit for the adductor muscle. The scuta 

 largely overlap the terga. 



Terga (fig. 3 b) approaching to rhomboidal ; basal angle 

 rectangular, almost central, and consequently the exterior 

 longitudinal ridge, winch is rounded, is likewise nearly 

 central. 



Carina, internally concave, with no trace of a central 

 internal ridge in the upper free portion ; the growing 

 or corium-covered surface is transversely oval, and is as 

 wide as the widest part of the terga. 



Rostrum, exceedingly minute, enlarged at each zone of 

 growth, not so wide as the immediately subjacent scale 

 on the peduncle. 



Latera (fig. 3 c), in width equalling two and a half of 

 the upper peduncular scales, or about one fourth or one 

 fifth of the width of the carina ; growing surface, (or a 

 section parallel to the layers of growth,) broadly elliptic, 

 pointed at both ends. 



Peduncle, about twice as long as the capitulum; the scales 

 of the uppermost whorl are quadrilateral (fig. 3 d), and 

 nearly four times as large as those in the second whorl ; 

 these latter are about twice as large as those in the third 

 whorl, which are very little larger than the small, almost 

 equal-sized, equally distant, round beads scattered over 

 the rest of the peduncle, down to the basal cup. All 

 these scales are dentated, the upper rows most plainly 

 and only on their basal margins ; the lower little beads 

 are very slightly crenated round their entire margins ; 

 they are mingled with star-headed spines (fig. 3 e) of yellow 

 chitine. Basal calcareous discs thin, plainly marked ex- 

 teriorly by concentric lines of growth, and covered by the 

 usual yellow membrane, including the horny, spindle- 

 shaped bodies. 



Size and Colours. — The whole specimen, including the 

 peduncle, was only one fifth of an inch in length ; the 

 capitulum being ^ths of an inch in width. I do not know 

 whether the specimen had attained its full size, but think 

 this is probable, as a large-sized species would not have 



