408 G. 0. SARS, [t. XIII 



what remote from the tip, apical sinus (see fig. 15) rather shallow, though 

 well-defined, and bordered by about 24 regular dentiform projections acute 

 at the tip, terminal lobes slightly diverging, and each tipped by a rather 

 strong spine. Inner lamella of the uropoda (fig. 13) moderately tumefied at 

 the base, with the otolith well-developed; inner edge armed, below the mar- 

 ginal setae, with about 9 spines, the outermost of which is placed at some 

 distance from the others, not far from the tip. Body without any distinct 

 dendritic ramifications, but having along the back the usual pigmentary 

 centres. Length of adult female reaching 2 1 mm. 



Remarks. — As above stated, this form was referred by Mr. Czer- 

 niavsky to his genus Paramysis. This is evidently quite erroneous, for it 

 is in all characteristics a true Mesomysis, as seen both from the above 

 description and the appended figures. In order to decide the question with 

 full certainty, I have felt justified to dissect one of the type specimens in 

 the collection of Czerniavsky. E>om the other species belonging to the 

 present genus, this form may at once be distinguished by its unusually 

 slender and elongated body, and the comparatively large telson. Besides the 

 typical form, Mr. Czerniavsky also records a variety „forma occidentalis" , 

 which, however, most probably is only founded upon an immature specimen 

 of the typical form. 



Occurrence. — According to Mr. Czerniavsky, 4 adult female speci- 

 mens of this form were collected by Lieutenant Uli sky in the mouth of the 

 Wolga, and thus probably in nearly pure fresh water. Another specimen 

 was, according to the same author, captured in the northern part of the 

 Caspian Sea, and a third immature specimen, that upon which the variety 

 „occidentalis" was founded, was apparently from Petrowsk or Baku. In the 

 collection of Warpachowsky this species was not represented. Except in 

 the Caspian Sea it has not yet been recorded. 



3. Mesomysis Kowalevskyi, Czern. 



(PI. IV). 

 Mesomysis KotcaievsJcyi, Czerniavsky, 1. c. fasc. 2, p. 50, PI. XXI, PI. XXII, figs 1 — 13. 



Specific Characters. — Body (PI. IV, fig. 1) not nearly so slender as in the 

 preceding species, and having the metasome much less prolonged. Carapace 

 evenly emarginated posteriorly, cephalic part fully as broad as the 1st seg- 

 ment of metasome, its anterior edge (see fig. 2) somewhat arched in the 

 middle, without, however, obtecting the frontal spine, which projects freely 

 beyond the edge. Eyes (ibid.) rather large, pyriform, projecting somewhat 

 beyond the sides of the carapace, corneal part well-developed, and, as usual, 

 emarginated on the dorsal face. Antennal scales (fig. 3) resembling in shape 



bulletin N. S. IY (XXXVI) p. 60. 



