26 G. O. SARS. M.-N. Kl. 



strong, with a distinct denticle at the base. Tail in male somewhat nar- 

 rower, with the postanal angle obtuse, being deeply sinuated below the 

 latter. Colour yellowish brown. Length of adult female 0,40 mm., of 

 male 0,27 mm. 



Remarks. This form has been described by Mr. Richard as a species 

 of the genus Plcnroxus. In my opinion, it is, however, a true Chydonis, 

 exhibiting, as it does, all the essential characters of that genus. From the 

 other known species it is easily distinguishable by the very conspicuous 

 curved striae on the anterior part of the valves, the serrated expansion of 

 the labrum, and by the presence of a distinct denticle on the infero- 

 postcal corners of the carapace. 



Description of the female, 



The length of adult,^ oviferous specimens does not exceed 0,40 mm., 

 and this form is accordingly of very small size. 



The general form of the body (see figs. 9 & 10) is that characteristic 

 of the genus, being very short and stout, almost globose. 



In a lateral view of the animal (fig. 9), the carapace exhibits a very 

 broad irregularly rounded form, with the greatest breadth about the 

 middle, and the posterior extremity narrowly truncated. The dorsal mar- 

 gin forms, along with that of the head, a strong and quite even curve, 

 whereas the inferior edges of the valves are abruptly bent in the middle, 

 forming an almost angular protuberance, behind which they are straight 

 and obliquely ascending towards the infero-posteal corners. In front of 

 the median protuberance, the inferior edges are slightly arcuate and join the 

 anterior ones by a strong curve. The posterior edges are straight and ver- 

 tical, joining both the dorsal and ventral margin at an obtuse angle. Seen 

 from above (fig. 10), the carapace appears somewhat less broad, and termi- 

 nates, posteriori}', in an obtuse point. 



The head, as in the other species of the genus, is procumbent and 

 to some degree mobile, admitting of being bent in against the anterior 

 part of the valves. Seen lateral]}^ (fig. 9), it tapers to an acute, but not 

 very elongate, and slightly curved rostrum. In a dorsal view of the 

 animal (fig. 10), die head appears very broad, on account of the greatly 

 prominent fornix, and of an almost semicircular form. 



The surface of die valves exhibits a very distinct sculpture, their 

 anterior part being provided widi about 10 curved transverse striae, 

 which run parallel to the anterior edge, and are very conspicuous. In the 

 posterior part the \^alves appear reticulated ^\•ith oblong rectangular meshes. 

 On the dorsal |)art of the carapace scarcely any sculpturing is traced. 



