MARINE ISOPODA OF NEW ENGLAND, ETC. 329 



or spines. The pleopods are protected by a thickened opercular plate, 

 and the uropods are short and simple or biramous. The incubatory- 

 pouch in the females is beneath the lirst four thoracic segments. 



Of this family, tvro species have been found on the Xew England 

 coast, and a third, from the Gulf of St. Lawrence, is here included. 

 The specimens obtained have been mostly in*poor condition, and one of 

 these, belonging apparently to an undescribed species, is so imperfect 

 that I have decided to await the collection of better specimens before 

 attemiiting a specific description. In the family characters given above, 

 as well as in the following generic and specific descrix)tions, I have 

 availed myself largely of the admirable works of M. Sars and his son 

 G. O, Sars, the distinguished Norwegian naturalists, to whom science is 

 indebted for the discovery and characterization of the present group. 



The Munnopsidcv of our coast may be easily recognized as belonging 

 to the family by the structiu'e of the last three pairs of thoracic legs, 

 which are fitted for swimming by being more or less flattened and ciliated ; 

 the last pair, however, may return to the more normal type of leg, so 

 that the fifth and sixth pairs only may be natatory. The three genera 

 which appear to be represented are distinguished as follows: Body sud- 

 denly constricted and slender behind the fourth thoracic segment in 

 Munnopsis (p. 329); pretty regularly oval in form, with three pairs of 

 flattened natatory legs in UKrycojje (p 38) ; suboval but deeply incised 

 behind the fourth segment, in Ilyarachna (p. 40), in which genus the last 

 pail' of legs are scarcely at all flattened or ciliated . 



Muunopsis M. Sara. 



Munnopsia M. Sars, Christ. Vid. Selsk. Forh., 1860, p. 84, 1861 ; Christ-fjord 

 Fauna, p. 70. 186S. 



Anterior division of the body dilated, posterior suddenly much nar- 

 rower and linear. Antennulse with the basal segment large and flat- 

 tened, the flagellum elongate and multiarticulate ; antennae very long 

 and slender, many times longer than the body; the last two peduncular 

 segments greatly elongated ; the flagellum about equal in length to the 

 peduncle ; mandibles subtriaugular, entire and acuminate at the apex, 

 without a molar i)rocess ; the x)alpus slender with the last segment thick 

 at the base and curved in the form of a hook ; penultimate segment of 

 the maxilliped not dilated inwardly; last segment very narrow and 

 linear. Four anterior thoracic segments excavated above, obtusely 

 rounded at the sides; the thi-ee following subcylindrical with short 

 acuminate lateral processes ; first four pairs of thoracic legs six-jointed 

 (beyond the coxal segment), the first pair short; the second pair not 

 much longer, rather robust and subprehensile in the males; the two fol- 

 lowing pairs greatly elongated and very slender, many times longer than 

 the body; but with the basis, ischium, and merus very short; last three 

 pairs of legs natatory, all alike, six-jointed, being destitute of dactyli, 

 with the last two segments, the carpus and propodus, foliaceous, mar- 

 gined with long, slender, delicately plumose setae. Pleon elongate, much 



