30 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 21, 



3. H. BiLOBUS, sp. nov. Fig. 1. 



H. 6-7-uncialis, ovato-elongatus ; articulis 11 vel 12, omnibus transversis, 

 ultimo subquadrato ; cauda oblonga, ad apicem profunde divisa. 



Of H. hilohus, which is the common species at Lesmahago, we 

 have more materials for illustrating the generic characters than of 

 any of the others. There are complete specimens with the head, 

 five or six thoracic, and six abdominal rings, tail, swimming-feet, 

 and antennae all in their places ; and several specimens show these 

 various parts dissected. It is only in this species that we can see 

 the maxillae in their right position, with their serrate edges and 

 broad foliaceous basal joints. The antennae also (probably only one 

 pair) are in their position, attached to the anterior part of the head. 

 They are linear, of few joints, and are deeply chelate at the tip. The 

 swimming-feet, attached to the posterior parts of the cephalic shield, 

 are short ; the portion which projects from beneath the carapace, 

 and is directed backwards, being not above one-fourth the entire 

 length of the body, and reaching to the fifth ring. The speci- 

 mens being all nearly of a size, it is presumed we have the adult 

 form. 



The body, in our best specimens, is elongate-oval in front, and 

 gradually attenuated into the abdomen, from which it is not easily 

 distinguished. If we reckon the five * anterior rings for the tho- 

 racic ones, these are widely transverse, the length even of the last 

 ring being not more than one-third its width. Their posterior angles 

 are very slightly produced backwards. The six posterior rings are 

 all much wider than long, except the penultimate joint, which ap- 

 proximates to square. Its hinder angles are produced to lap over the 

 rounded anterior edges of the caudal joint. The latter is only two- 

 thirds as wide as long, and fully double the length of the penulti- 

 mate joint. It is widest behind, with the posterior angles rounded 

 off, and is deeply cleft more than half way up. No median keel 

 like that of H. acuminatus can be detected on any of the body-joints 

 except the last but one ; the upper part of the tail is keeled also for 

 a short distance. 



The carapace is half-oval, and only one-fifth wider than long. 

 The position of the eyes is very forward on the sides, and they some- 

 ^ what interrupt the general oval contour. They are broadly cres- 

 centic and convex ; and their extreme length is rather more than 

 half that of the head. No lenses can be seen on their smooth sur- 

 face. 



The maxillae (or mandibles) occupy nearly all the under side of 

 the head ; they are 4-jointed ; the basal joint greatly the largest, 

 and somewhat of a spherical-triangular form ; the second and third 

 joints are narrow and wedge-shaped, and the terminal one short and 



* Or six. There is some evidence of a narrow anterior segment in addition to 

 the eleven body-rings ; and, as three other species have the anterior segment 

 narrow, and eleven rings behind it, it is probably the case here ; and we have 

 so represented it in the diagram (fig. 1, p. 28). 



