256 THE VOYAGE OF H.M.S. CHALLENGER. 



This species, since first described by Dana, does not appear to have been identified 

 by any naturalist except Stimpson ; it is so much like Penseus affinis, Milne- 

 Edwards, that it has probably been mistaken for it, as in general appearance the species 

 correspond. 



Penseus barbatus, de Haan, 1 differs from it in the number of teeth on the rostrum, 

 which is figured with eight, the posterior of which is distant from the others and 

 described " Rostro margine . . . ., superiore 5-7 dentato ; " the greater length of the 

 flagella of the first pair of antennas, and in having " Pedes tres antici basi unispinosi;" 

 a circumstance that separates de Haan's species from those that I have described (as 

 Penseus velutinus) from off the southern coast of Japan. They may however with 

 certainty be distinguished by several important points, of which the following are the 

 most conspicuous. 



The rostrum in Penseus velutinus is not cmite so long in relation to the length 

 of the carapace, the denticulation on the upper surface is deeper and closer, and the 

 rostrum greater in depth and less styliform at the extremity. The flagella of the first 

 pair of antennas are shorter. The first pair of pereiopoda is armed with two strong 

 teeth, and the second pair with one. In the female two long slender teeth project from 

 the ventral surface of the somite between the second pair of pereiopoda ; which, together 

 with a variation in the form of the petasma attached to the first pair of pleopoda 

 in the male, are decided points of specific separation. 



Dana dredged his specimen off the Sandwich Islands, but records it as being only 

 one and three-quarters of an inch long, or about one-half the length of those taken 

 by the Challenger, excepting in the case of a few young ones, which I presume Dana's 

 specimen must have been. 



At Station 190 numerous specimens were taken, ranging in sizes from 25 mm. to 

 75 mm. The adult male corresponds with that of our type, except that it has the longer 

 branch of the petasma tipped with radiating points ; in the younger forms the extremity 

 of that organ is smooth and not prolonged, and in a still younger male the two branches 

 are separate and narrow. The females also correspond with the same sex in the typical 

 specimens, except that the two spinous teeth between the second pair of pereiopoda are 

 short in the younger specimens, and in some they appear to be absent. 



These may be recognised as a variety under the name of radiata. 



The following species exhibit a resemblance in external form to Peweus velutinus, 

 the variation in the number of teeth on the rostrum being inconsiderable, and in my 

 opinion of secondary importance, and they each carry a solitary tooth planted on the 

 gastric region, varying a little in position, being more or less distant from the posterior 

 tooth on the rostrum. Notwithstanding this general similitude there are certain 

 important details that appear to me to be neither directly or immediately transmit- 



1 V. Siebold's Fauna Japonica, Crustacea, p. 192, Pennsus barbatus, pi. xvi. fig. 3. 



