9 



Pena?«s canna<us, Dana, U.S. Expl. Exp,, Cmst, pt. I. p. 602, pi. xl. fig. 2,1832: Heller, Novara Crast. 

 p. 123: Walker, Journ, Linn. Soc, Zool. XX. 1887, p. 112. 



? Penasus eseuUntus, Haawell, P.L.S., N. S. Wales, 1879, p. 38, and Cat. Austral. Crnst., p. 200, 1882 : Stead, 

 Zoologist (4) II. 1898, p. 209. 



Penpeus ashiaJca, Kishinonye, Jonrn. Fish. Bur., Tokyo, VIII. i. 1900, pp. 7, 14, pi. iii : Eathbun, Proo. U.S. 

 Nat. Mns. XXVI. 1902, p. 38 : Nobili, Boll. Mus. Torino, XVITI. 1903, No. 455, p. 2. 



The species here described and figured is the P. monodon figured in the 

 Challenger Report : it differs from DeHaan's P. semisulcatus in having an exo- 

 podite on the last pair of thoracic legs. It is not the P. monodon of authors in 

 general which appears to include P. monodon and P. semisulcatus. 



Rostrum nearly straight, rarely reaching to, and still more rarely beyond, 

 the tip of the antennular peduncle in the adult, though in the young it may be 

 relatively longer: dorsally it has 6-8 (usually 7) teeth, ventrally 8. The 

 dorsal teeth form a keel or crest of moderate height, which is continued as a 

 deeply-grooved post-rostral crest to about one-third of an eye-length fi'om the 

 posterior border of the carapace : on either side of the crest is a groove, which 

 ends just behind the last (epigastric) tooth. 



The cervical groove is defined only in the neighbourhood of the hepatic 

 spine, wherd' it is deep. 



There is no post-ocular spine; but the post-antennular ("antennal") spine 

 is strong, and is continued obHquely backwards as a sharp ridge to the base 

 of the strong hepatic spine. Above and parallel with this post-antennular 

 crest is another short ridge, post-orbital in position, which meets the cervical 

 groove; and between these two ridges is a deep post-antennular sulcus, more 

 or less filled with tomentum, which undermines the hepatic spine. The 

 branchial region is defined anteriorly by an oblique ridge and groove, which run 

 from the base of the hepatic spine towards the base of the antenna. 



The 4th — 6th abdominal terga are carinated in the middle line, the 4th 

 in its posterior three-fourths only; and the carina of the 6th ends acutely. 

 The 5th abdominal somite is about two-thirds the length of the 6th, and the 

 6th is a httle shorter than the telson. The lateral borders of the telson are 

 non-spinose. 



The antennular scale reaches well beyond the eyes : the upper or outer 

 (longer) antennular flagellum is very considerably shorter than its peduncle. 



The antennal scale reaches hardly half an eye-length beyond the tip of the 

 antennular peduncle. 



The external raaxillipeds reach to the anterior third of the antennal scale : 

 their dactylus, in the adult male, is about as long as the propodite, from 

 the inner side of which it arises : from the tip of the propodite springs a pencil 

 of setK which can be lodged in the concave inner side of the dactylus ; the tip 

 of the dactylus is bluntly rounded. In the female the dactylus is a tapering 

 joint articulating in the ordinary way end-on with the propodite. 

 2 



