MUSEUM OF COMPARATIVE ZOOLOGY. 91 



From Station 325, there is the crushed and fragmentary cephalothoracic 

 portion of another specimen, apparently of this species, but having two teeth 

 on the crest of the rostrum, the second tooth being about half-way between the 

 one above the posterior margin of the orbit and the tip of the rostrum. 



This species has also been taken by the U. S. Fish Commission at the fol- 

 lowing stations oflf Block Island, in 1880 and 1881 : — 



Among these were the only specimens which had either of the fourth and 

 fifth pairs of legs, the telson, or the uropodal lamellae perfect. 



The specimens in alcohol retain for a considerable time bright purple mark- 

 ings about the oral appendages, and give out a peculiar, bright red, oil-like 

 fluid, after the manner of the species of Sergestes and some of the deep-water 

 Schizopoda. 



Hymenopenseus debilis, gen. et sp. nov. 



Plate XV. Figs. 6-11. Plate XVI. Figs. 1-3. 



The whole integument is membranaceous and exceedingly thin and soft. 

 The carapax is smooth, naked, slightly compressed laterally, and dorsally cari- 

 nated the whole length but not conspicuously on the posterior part ; there are 

 four large and acute lateral spines either side, — an antennal, an hepatic, one a 

 little way back of the antennal, and another (branchiostegial ?) below and in 

 front of the hepatic and near the lower edge of the carapax ; the gastro-hepatic 

 sulcus is conspicuous and deep, and continues upward to the dorsal line con- 

 siderably back of the middle of the carapax and terminates below in front of 

 the hepatic spine in a depression from which a narrow sulcus extends backward 

 and divides, sending a short branch downward in front of the branchial region 

 and a long one back to become the cardiaco-branchial. The rostrum is nearly 

 straight, a little less than half as long as the rest of the carapax along the 

 dorsum, compressed but not high, terminates in an acute point, is armed 

 above with six or seven teeth besides three more widely separated and nearly 

 equidistant ones upon the anterior half of the carapax proper, and near the tip 

 below with a closely set series of hairs. 



