116 C. F. ROUSSELET ON LITTLE- KNO^YN PTERODINA. 



resemblance with reftexa, but if correctly described it can be 

 •distinguished by the following characters : Pt. incisa has the sides 

 still more turned upwards, forming an angle of nearly 90°, and 

 the margin is thin according to Ternetz's drawings, which I have 

 reproduced in Fig. 8 a and b, and not rounded and thick ; further, 

 the dorsal anterior edge has a deep rounded sulcus as well as 

 the mental edge, and the lateral antennae are situated more 

 anteriorly. 



The internal anatomy of Pt. reflexa is normal and well repre- 

 sented in Mr. Dixon-Nuttall's drawing. Fig. 5a. 



Size : length of lorica yiy in. (150 /x), width o-g-Q in. (98 ja). 



Pt. elliptica Ehrbg. Plate 4, Fig. 4. This species has never 

 been well defined by Ehrenberg, and is scarcely differentiated in 

 Hudson & Gosse's monograph, where it is represented only by 

 the doubtful figure of an empty lorica. It is, however, a well 

 •characterised species, which I have often found living a parasitic 

 or rather commensal life on the legs and gill plates of Asellus 

 vulgaris. It is the largest of the various species with thickened 

 •edges. The lorica has the form of a long oval with somewhat 

 flattened anterior dorsal margin ; the mental edge has the form 

 of two semicircular lobes, with a deep acute sinus between them, 

 -as seen in Fig. 45. The shell has considerable thickness, and its 

 exact shape will best be understood by reference to the transverse 

 section. Fig. 4:d ; the edges are thick and rounded all round, 

 increasing in thickness posteriorly ; the dorsal surface as a whole 

 is slightly convex, with two depressions between the rounded edges 

 and the higher central region ; the ventral surface has the 

 central part projecting with a longitudinal shallow groove on 

 each side. 



The foot opening is close to the posterior edge on the ventral 

 side, and half-moon-shaped. The lateral antennae are high up on 

 the shoulders, and the very small dorsal antenna, not before 

 ■discovered, was found, situated in the middle Ime just above the 

 mastax when the animal is fully extended; it is found in the 

 same position in all species of Pterodina. Two large elongated 

 gastric glands are conspicuous in this species ; fixed to the 

 anterior part of the stomach, they lie at right angles across the 

 body on each side, and appear to be attached near the edges of 

 the lorica. A second pair of smaller gastric glands are situated 

 just above the others, and show a number of large nuclei. The 



