334 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



This species was dredged by Mr. J. F. Wliiteaves in the Gulf of St. 

 Lawrence ! at a depth of 220 fathoms muddy bottom, and has not yet been 

 found on the coast of New England. It is introduced here from the 

 l^robability that it will yet be discovered in the deeper parts of the Bay 

 of Fuudy, where the allied Munnopsis typica M. Sars has already been 

 found, or even in the Gulf of Maine. 



Specimens examined. 



Ilyarachna G. O. Sars. 



Mesostenus G. O. Sars, Clir. Vid. Selsk. Forh., 1863, p. 211, 1864. 

 Ilyarachna G. O. Sars, Christ. Fjord. Dybvands-fauna, p. (44), 1869. 



Body scarcely depressed, subpyriform as seen from above, narrowed 

 behind; its anterior division separated from the posterior by a deep 

 constriction. The head is large and broad and without a rostrum. 

 Antennuli© short, with a flagellum composed of but few segments. An- 

 tennse exceeding the body in length, with a multiarticulate flagellum. 

 Mandibles short and strong, entire at the apex ; molar process armed 

 with a few setiform spines ; palpus either small and three-jointed or want- 

 ing. Four anterior thoracic segments short, excavated above and fur- 

 nished with lateral processes directed forward; the three following 

 convex above and destitute of lateral processes ; the antepenultimate 

 scarcely narrower than the anterior segments and deeply emarginate 

 behind. First pair of legs nearly as in the preceding genus ; second 

 pair unlike the others and usually more robust ; the following two sub- 

 equal and commonly much elongated ; fifth and sixth pairs of legs much 

 as in Uiiryeope; the last pair unlike the preceding, long and slender, 

 with the segments scarcely flattened, and armed with a long curved claw. 

 Pleon narrowly triangular, pointed at the apex. Abdominal operculum 

 large, covering nearly the whole of the under surface of the pleon, pro- 

 vided with a median crest and numerous marginal setse. Uropods simple, 

 appressed to the pleon. 



For the generic description given above I have depended almost en- 

 tirely upon the work of Dr. G. O. Sars, who originally described the 

 genus under the name Mesostenus. That name being preoccupied he 

 subsequently changed it to Ilyarachna. 



