28 C. F. ROUSSELET OX LITTLE-KNOWX PTERODINA. 



living commensally on Asellus vulgaris, and was first described 

 by Mr. F. A. Parsons in our Journal of January 1892, but only 

 figured by a small outline drawing of the lorica. The accompany- 

 ing figures will, I hope, give a better and more accurate idea of 

 this small but interesting species. The lorica is egg-shaped, 

 truncate in front, the anterior dorsal edge prolonged into a 

 rounded cone, the mental edge is incised with a not very deep 

 acute sinus. The shell is thick, and has thick rounded edges. 

 which are slightly curved upwards ; the ventral side shows two 

 shallow depressions and the dorsal side two deeper ones, and the 

 whole shape of the lorica will best be understood by referring to 

 the transverse section, Fig. \d. 



The foot opening is situated quite close to the posterior ventral 

 edge ; it is broad and shield-shaped. The lateral antennfe are 

 very minute, but can be seen projecting near the edge of the 

 lorica a little above the middle ; the dorsal antenna was found 

 situated slightly higher on the middle line, above the mastax 

 when the animal is extended. The gastric glands are large, and 

 broaden out towards the edge, otherwise the internal anatomy 

 is normal. A great peculiarity of this species is that it has 

 no trace of eyes which are so prominent in all other species. 

 Pt. Coeca has been obtained mostly from Epping Forest. Fig. le 

 represents the jaws, drawn by Mr. Dixon Nuttall. 



Size of lorica : yi^ in. (170 ^) by —^ in. (108 fx) broad. 



There is yet another species which habitually takes up its 

 quarters on Asellus — namely Pt. truncata (Gosge), mentioned 

 by Mr. Gr. Western in our Journal for July 1893, p. 155, and 

 figured in outline on PI. XXV., Fig. 4 (Quekett Journal, 

 January 1892). The animal figured by Dr. W. Barnett-Burn 

 under the same name in Science Gossi]), 1889, p. 104, is, I 

 believe, Pt. elUiitica. Mr. Western maintains that Pt. truncata 

 is a distinct species ; it is certainly very closely allied to Pt. eUijytica, 

 if it is not identical with it. 



In 1892 Dr. Ternetz described a new species, Pt. Indentata, 

 which has lately also been found in England by Mr. John Hood 

 and Mr. Dixon-Nuttall. It has a flat and nearly circular lorica, 

 but is remarkable in having a large thorn on each side of the 

 latero-posterior margin. In 1893 Prof. Wierzejski described the 

 same species under the name of Pt. emarginata, and it has also 

 been observed by Forstmeister Bilfinger in Wllrttemberg. The 



