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



terminating in a small tooth. Telson long and pointed, dorsally channelled, and laterally 

 armed with a strong tooth and with some hairs on each side. 



The ophthalmus is large, oblong, and reaches to nearly the extremity of the rostrum. 



First pair of antennae having the peduncle extending considerably beyond the 

 rostrum. The flagella unequal ; the longest being half the length of the peduncle, the 

 shortest half its length. 



Second pah' of antennse about once and a half as long as the animal, and the 

 scaphocerite reaching beyond the extremity of the peduncle of the first pair. 



The first pair of pereiopoda has a tooth on the infero-anterior angle of the basis, and 

 another on the same position on the ischium ; the second and third pairs are unarmed. 



A linear fissure longitudinally traverses the carapace on each side, from the orbit to 

 just within the posterior margin of the carapace, and a similar but shorter fissure vertically 

 divides the branchial margin opposite the third pair of pereiopoda. 



Length of female, 105 mm. (4*2 in.). Male, 85 mm. (3 - 4 in.). 



Habitat.— Station 190, September 12, 1874 ; lat. 8° 56' S., long. 136° 5' E.; depth, 

 49 fathoms ; bottom, green mud. One male ; two females. Trawled. 



Station 204a, November 2, 1874; lat. 12° 43' N., long. 122° 9' E.; off Tablas 

 Island; depth, 100 fathoms; bottom, green mud. 



Station 204b, November 2, 1874; lat. 12° 46' N., long. 122° 10' E.; off Tablas 

 Island ; depth, 115 fathoms ; bottom, green mud. Two females. Trawled. 



Station 209, January 22, 1875; lat. 10° 14' N, long. 123° 54' E.; off Zebu; depth, 

 95 to 100 fathoms; bottom, blue mud; bottom temperature, 71°. Ten specimens. 

 Five males, five females. Trawled and dredged. 



This form approximates closely to Penseus monoceros, Fabricius, the most apparent 

 distinctions being that Penseus monoceros has nine teeth on the dorsal surface of the 

 rostrum, whereas Penseus Jissurus has six, and the telson has a strong tooth on each side, 

 while Penseus monoceros has none. 



I have utilised this peculiar fissure as a name to the species so that it may receive 

 the attention of naturalists. I have also seen it in a species, allied in form to Penseus 

 affinis, in the Museum of the Jardin des Plantes. I do not know its value, but am 

 inclined to think that it is not of much specific importance, and may be caused by an 

 approaching moult; of this, however, I have no experience to guide me, as in all forms 

 that have been observed, excepting in the Brachyura, the carapace is thrown off 

 entire. 



The rostrum is about one-third the length of the carapace and horizontal ; it is 

 armed with six teeth, and one on the gastric region, from which the dorsal carina extends 

 to the posterior margin of the carapace. The frontal margin is hollowed close to the base 

 of the rostrum, on the outer side it projects and is produced to a small tootb, from near 



