22 FOSSIL IMALACOSTRACOUS CRUSTACEA. 



regards those joints which remain, arc all simple and somewhat rounded, ha\ing no 

 appearance of the flattened, paddle-shaped form, which is an obvious feature in most 

 of the Portunidae. The flatness of the carapace, its form and sculpture, and the number of 

 marginal processes are, however, in perfect coincidence with the structiu-e of that family; 

 and there is another incidental peculiarity which confirms this view, the habit, namely, of 

 turning the hinder leg over the back when not employed, as is seen in the figui-e ;* and 

 this habit is, as it were, provided for by a longitudinal ridge running the whole length of 

 the metabranchial lobe, against which the third or principal joint of the leg rests ; 

 a peculiarity which I do not remember to have seen in any recent form. 



Sub-Order— CATAMETOPA. 



Fa?nily—THELVn\]SA.'D/E ? 

 Gemts — CEdisoma, SsH. 



Species unica. (Edisoma ambigudm, mi//i. Plate III, figs. 6, 7. 



Descr. The only certain specimen I have seen of this singular little Crustacean is in the 

 collection of Mr. Bowcrbank, from Sheppey, and consists of a tolerably perfect body, but 

 without limbs or abdomen. The carapace is perfectly smooth, its general form ovoid, 

 the latero-anterior and latero-posterior margin smooth, rounded, and without armature ; 

 the gastric region distinct, the protogastric lobes rounded, the meso- and metagastric 

 undistinguished, and forming together an elongate pentagon ; cardiac region somewhat 

 rhomboidal ; hepatic region extremely small ; branchial very largely developed and tumid. 

 Orbits large, oval, opening directly forwards, and extending laterally to within a foiu'th of 

 the half breadth of the carapace on each side ; the epistome is regularly rhomboidal ; 

 the external footjaws appear to have been sculptured, but the worn state of the specimen 

 prevents the details or even the general form of these parts from being made out. The 

 remains of the basal portion of the antennae only indicate that these organs were of large 

 size, and that they closed the hiatus of the orljit. 



Length of carapace, 0"3 inch ; breadth, 0-5 inch nearly. 



0/js. These are the meagre data on which I have ventured to found the present 

 genus. The Uttle specimen certainly belongs to no knoum generic form, and even 

 its family affinities are not very oljvious. I have, however, ventured to give it a 

 provisional place among the Thelphusadse, which the occurrence of more perfect specimens 

 may at some future time either correct or confirm. 



* Plate II, fig. I. 



