CRUSTACEA CASPIA. 309 



f 28. Corophium monodon, G. 0. Sars, n. sp. 



(PI. XXIV, figs. 8-16). 



Specific Characters. — Body rather slender, especially in the male. 

 Frontal edge of cephalou angularly produced in the middle, lateral lobes 

 narrowly rounded. Urosome with all the segments well defined. Superior 

 antennae of moderate length, and not very different in the two sexes, though 

 the peduncle in male appears somewhat more elongated and more densely 

 setous, 1st joint of the peduncle in both sexes longer than the other 2 com- 

 bined, and having at the end below a single spinule; flagellum in female 

 about the length of the peduncle, in male somewhat shorter. Inferior antenuje 

 in female rather small and feeble, scarcely longer than the superior ones, in 

 male much more elongated, exceeding % of the length of the body, pen- 

 ultimate joint of the peduncle long and slender, almost cylindric in form, 

 being produced at the end posteriorly to a narrow mucroniform projection 

 not extending to the middle of the last joint, and having no secondary tooth 

 at the base ; last peduncular joint with only a very slight rudiment of a tooth 

 near the base posteriorly; tiagellum very short, scarcely exceeding half the 

 length of the former joint. Anterior pairs of pereiopoda somewhat more 

 slender than in G. mucronafum, meral joint gradually widening distally, and 

 provided anteriorly with scattered bristles. Last pair of pereiopoda with the 

 basal joint rather expanded, the outer joints, however, narrow and slender. 

 Uropoda and telson of the usual structure. Length of adult female 4 mm., 

 of male 5 mm. 



Bemarls. — Of all the Caspian species, this one would seem to come nearest 

 to the tn)ical species, C. grossqies, Lin. It is however evidently specifically 

 distinct, differing, among other characters, in the much less strong develop- 

 ment of the inferior antenna^, the penultimate peduncular joint of which is 

 far loss tumefied, and wants the deep sinus occurring iu that species at the 

 base of its terminal projection. 



Description,. — The length of fully adult, ovigerous females does not ex- 

 ceed 4 mm., that of the male being 5 mm., and this form accordingly is the 

 smallest of the Caspian species, and in this respect is also rather inferior to 

 the typical form, C. grossijU'S, Lin. 



The form of the body (see fig. 8) is rather slender, especially in the male, 

 otherwise of the usual appearance. 



The cephalou has the frontal edge (see fig. 9) distinctly produced iu the 

 middle, forming an almost right angle. The lateral lobes are not very promi- 

 nent and they are, as in the other Caspian species, narrowly rounded at the tip. 



Tlie coxal and epimeral plates are of the usual shape. 



^H3.-MaT. CTp. 217. 35 



