382 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



ocular spines. The rostrum is short, subacute, broader at base than loug, feebly convex aoove, 

 without crest. The orbital spines are separated from the rostrum by a shallow superlicial groove, 

 and the marginal notch on each side has a regular V/shaped outline. Length of siiines and width 

 of notch are slightly variable. 



The lateral compression of caiapax is not marked. Frontal angle (angle made by middle line 

 above and below rostrum, greater in 9 than in S . In some females with the carapace bulged out 

 by the ovaries the angle is as great as 45°. In males without conspicuous "forehead'' frontal 

 angle, 10°. 



The telson ends bluntly. It is two-thirds as broad as long, and twice as broad at base as at 

 apex. There is a single pair of short spines at the posterior extremity on either side the middle 

 line, and two (or more) separate spines upon either side further forward. There is a wide and 

 shallow^ median dei)ression. 



The compound eye§ are conspicuous, owing to their dark pigment and the transparency of the 

 carapace, and in the largest adults they show no traces of degeneracy. There is a i^ermanent 

 ocelluii [P]. XXII, Fig. 18), which occupies the same position and has the same characters as at birth. 

 It consists of a pigmented body embedded in a short median papilla, situated below the compound 

 eyes and between the bases of the antennules. 



The antennules (Fig. 4, PI. xxiii) consist of a three-jointed stem or protopodite, an exopodite, 

 and endopodite. The first segment of the stem is largest and bears an external spine (aural spine), 

 which protects the auditory sac. The latter is large and conspicuous Jn this genus. It usually 

 contains some pigment cells and grains of sand. Second segment about half as long as first; 

 third, four-fifths as long as second. Endopodite one and one-half times the length of stalk, slender. 

 Exopodite compound, a slender flagellum branching from near the end of the stouter proximal 

 portion. On the uiKler side of the latter the sensory filaments (olfactory seta") are borne, distrib- 

 uted in seven to ten bunches of two to three in a bunch. 



The antenna; (Fig. 8, PI. xxiii) are composed of three parts — a basal portion (protopodite), 

 which carries a squamous spine (exopodite), and on its inner and lower side a long three-jointed 

 stem, whii h bears a flagellum (endopodite). 



The protopodite consists of a proximal segment (coxopodite) and a larger distal one (basipo- 

 dite). A prominent papilliform process is seen on the inner side of the coxopodite at its point of 

 junction with the basipodite. Upon it the duct of the green gland probably opens to the exterior. 

 The basipodite is continued into a prominent spine below and into one or more rudimentary sjiurs 

 above. To it is articulated a long, stout, scale-bearing spine. The scale plate, usually shorter 

 than the spine and attached to it for less than half its length, is fringed on its inner free edge with 

 idumose setic. The antennal stem or peduncle consists of two short i)roximal segments and a loug 

 distal one, which carries the multarticulate flagellum. The latter is often hairy, and is two to 

 three times the length of the peduncle. The relative lengths of the different parts for an average 

 specimen is shown in Fig. 8, PI, xxm, and in PI. iv. 



The mandibles (Fig. 3, PI. xxiii) are strongly bifurcate, as is characteristic of the genus. The 

 larger division is finely tuberculated, while the masticatory surface of the slenderer branch is 

 raised into sharp teeth. This bears a jointed palp (endopodite) on the inner side. The mandibular 

 palpus is short; its terminal segment large and hairy. 



The first maxilla (PI. xxiv, Fig. 7) consists of three divisions — a smaller branch (endopodite), 

 a larger branch (basipodite), divided at the apex and terminated by several long spines, and a 

 larger spatula-shaped fork, the maxillary surface of which is beset with spines (coxopodite). (v. 

 Description of figure.) 



The second maxilla (PI. xxiv, Fig. 9) is composed of three portions. (1) The long respiratory 

 plate; the "bailer" or scaphoguathite, fringed with a row of setae. (2) An outer and lobulatcd 

 division (coxopodite and basipodite), the inner edge of which are closely set with bristles, and (3) 

 a median rudimentary endopodite. 



The first pair of maxillipeds (Fig. 7, PI. xxiii) are made up of a long, strap-shaped exopodite, 

 with jointed sette at the extremity and a small setigerous plate at its base; a small, two-jointed 

 endopodite, protopodite, aud epipodite. The protopodite is divided by a fissure into two lobes, a 

 larger (basipodite), with dense rows of bristles on its maxillary surface, and a smaller division 

 (ci)X(ipodite). The epipodite is an oblong plate, united by a short stalk to the protopodite. 



