408» PALEONTOLOGY OF NEW-YORK. 



The posterior lateral angles of the joints, from the bixth to the tenth, 

 are usually salient, and projecting backwards in a spiniform process. The 

 three first pairs of feet are similar in form, consisting of broad strong 

 joints ; the angles of the more extreme joints (and perhaps of all ) fur- 

 nished with smooth spines, usually on one side, while the two preceding 

 the last one are furnished with a spiniferous process on each distal angle ; 

 the last joint being a simple smooth chelate tip. Each pair in succession 

 is a little longer than the preceding, and the third pair proportionally 

 longer than the second. The fourth pair is more slender, but strongly 

 jointed ; fully once and a half as long as the third : the last joint is a 

 long smooth slender chela, and each of the distal angles of the penulti- 

 mate joint is furnished with a slender chelate tip, while the other joints 

 of the same have shown no such processes. 



The swimming feet are strongly articulated to broad rhomboidal ma- 

 xillary plates : the anterior distal angles of the [third], fourth, fifth and 

 sixth joints are acutely angular, and project over the next joint in ad- 

 vance ; the first joint is broadly dilated, and the penultimate is ovate and 

 shorter than its preceding. The two joints forming the pincers are nearly 

 as long as the five preceding joints, including the maxillary plate. The 

 terminal palette is very minute, and, inserted into the notch at the 

 extremity, scarcely extends beyond it. The anterior edges of these joints 

 sometimes show serratures. 



The post-oral plate is ovato-cordiform : crust thin, often finely wrin- 

 kled or striated, and both the dorsal and ventral sides of the thorax and 

 abdomen are marked by the peculiar scaly surface. On the dorsal side 

 these scale-like processes become developed into spiniform pustules, 

 arranged in longitudinal rows down the back ; there being usually four, 

 and rarely five or six rows visible on the thoracic segments, while the 

 abdominal segments preserve but two such rows. This feature is not 

 always visible, and the scales of the intervening parts are sometimes so 

 prominent as to interrupt the visible continuity of the lines. 



The greater number of specimens examined are imperfect, and but a 

 single specimen has showii the limbs entire. 



