MARINE ISOPODA OF NEW ENGLAND, ETC. 335 



Cyarachna species. 



A single imperfect specimen of a species apparently belonging to this 

 genus was dredged in 106 ftithoms, gray mud, 21 miles east of Cape Cod 

 Light!, September 18, 1879. The species is probably yet undescribed, 

 but, in xiew of the very imperfect condition of the only specimen yet 

 known, I have decided to await the collection of better specimens be- 

 fore attempting to make out its characters. It may yet be found to 

 represent an undescribed genus, but I am at i^resent inclined to regard 

 it as a species of Tlyaraclma. 



v.— IDOTEID^. 



Antennulse consisting of four segments, of which the basal is more 

 or less enlarged and^he terminal clavate ; mandibles not palpigerous j 

 thoracic segments subequal in length; pleon with more or fewer of 

 its segments consolidated into a large, scutiform, terminal piece; 

 uropods inferior, transformed into a two-valved operculum protecting 

 the pleopods. 



The Idotddce are represented on the New England coast by ten 

 species; another, found near our northern limits, is included, making 

 eleven in all, belonging to five genera. The family may be further 

 characterized, so far as regards our species, as follows : The body is 

 depressed, and varies in its proportions of length to breadth from 

 about two to one in CMridotea eoeca to nearly six to one in Urichsonia 

 attenuata. The head is quadrate in outline, except in CMridotea. The 

 eyes are present and usually lateral, but may not be conspicuous. 

 The antennulse are four-jointed and similar in form throughout the 

 family; they may or may not surpass the head in length, but are usu- 

 ally short and small. The basal segment of the antennula) is more or 

 less enlarged and usually subquadrate ; the second segment is clavate ; 

 the thu'd longer and less distinctly clavate; the fourth, or terminal, seg- 

 ment, corresponding with the flagellum of the antennulae, is nearly 

 straight along its outer, or in the natural position posterior, margin, 

 while the opposite margin is gently curved from near the base, and 

 rounds over more sharply at the tip ; along this margin, especially toward 

 the tip, are tufts of short setae at regular intervals, indicating an approach 

 toward segmentation. The antennae have a five-jointed peduncle, vary- 

 ing little in form throughout the family; the first of these segments is 

 short; the second is much larger and deeplj' notched on its under side; 

 the third, foiu-th, and fifth segments are longer, but more slender and 

 cylindrical or somewhat clavate. The flagellum of the antennae may be 

 articulated with many or few segments ; it may consist of a single seg- 

 ment, or may be rudimentary. The maxiUipeds are opercuhform and 

 cover the other parts of the mouth below. They consist, on each side, of 

 a large semi-oval plate, with a straight interior margin, meeting its fellow 



