CRUSTACEA CASPIA. 185 



fishes and other enemies. This may also apply to the above mentioned species 

 of AUorchestes, which do not seem to he very habile swimmers. 



Description of the female. 



(See PI. I). 



The length of the body in adult ovigerous specimens measures, when 

 fully extended, about 20 mm., and this Amphipod attains thus a rather 

 large size. 



The form of the body (see figs. 1 and 2) is extremely stout and compact, 

 more so than in any othei' known Gammarid, and all the integuments are 

 very hard and highly incrusted. In alcoholic specimens the body is generally 

 found to exhibit a strong curvature, the posterior part being folded in 

 beneath the anterior, and the head curved downwards. In this state it looks 

 like an irregular ball, from the centre of which projets on each side the 

 large mucroniform spine of the 5th segment. When fully extended, the back 

 remains still somewhat curved (see fig. 1), though the mutual longitudinal 

 relation of the several body-divisions now may easily be determined. It is 

 found that the mesosome occupies much the greater part of the body, the 

 metasome and urosome being comparatively poorly developed and combined 

 scarcely longer than the foi'mer division. All the segments of the body ap- 

 pear very sharply defined, and those of the mesosome are particularly broad 

 and subfornicate in shape, being produced on each side, just above the 

 junction of the coxal plates, to rounded prominences, each tipped by a later- 

 ally projecting spiniform process. The 4 anterior and 2 posterior pairs of 

 those processes are comparatively short and obtuse at the tip, whereas those 

 of the 5th pair are very large and prominent, mucroniform, and gradually 

 tapering to a very acute point. Along the back both the mesosome and 

 metasome exhibit a distinct, though somewhat obtuse keel, wliicli in each 

 segment is elevated to a rounded dorsal prominence, those of the segments 

 of the metasome being somewhat more compressed and sublaminar. In each 

 of the latter segments occur near the dorsal face a pair of upturned digiti- 

 form processes, which however on the 1st segment are generally very small 

 and merely tuberculiform. The 1st segment of the urosome (see fig. 5) is 

 comparatively large and of a somewhat trigonal form, being produced at 

 the end dorsally to a rather prominent and somewhat hooked projection, 

 fully overlapping the 2 succeeding very short segments, and even reaching 

 somewhat beyond the tip of the last pair of uropoda. At the base of this 

 projection occur a pair of subdorsal digitiform processes of a similar appea- 

 rance to those found in the posterior segments of the metasome. 



^Ha.-llIaT. CTp. 185. 7 



