1870.] WOODWABD lOWEE-EOCEins CRUSTACEA. 91 



II. Family PoKTinsriDiE. (Gen. nov. Bhachiosoma.) 



Amongst the pelagic Crustaceans we find numerous examples be- 

 longing to the Portunidse, aU armed with long spines on the hepatic 

 region, and with the lateral borders of the carapace greatly produced. 

 Thus the genera Matuta, Orithyia, Podophihalmus, Portunus, Lupea, 

 and many other forms possess long hepatic spines. 



Two Eocene genera have also been described and figured by Dr. 

 Alphonse Milne-Edwards in his 'Histoire des Crustaces Podoph- 

 thalmaires Fossiles,' namely, Enoplonotus armatus, from the Num- 

 mulitic beds, Salcedo, and the Psammocarcinus Hericartii (Plate IV. 

 fig. 4), from the Sables de Beauchamp (Lower Eocene). We are 

 now, by Mr. Meyer's exertions, made acquainted with two new 

 forms (see Plate IV. figs. 3 and 5) from the Lower Eocene of 

 Portsmouth, which it is proposed to place in a new genus, the 

 characters presented by the carapace in the specimens under con- 

 sideration not warranting us in referring them with certainty to any 

 genus of fossil Crustacea already established. 



Ehachiosoma*, gen. nov. 



Carapace produced laterally into two more or less long and 

 .pointed spines ; latere -anterior border also furnished with spines ; 

 surface of carapace tuberculated. 



1. Rachiosoma bispinosa, sp. nov. (Plate IV. fig. 3.) 



This form is remarkable for the great development of its two 

 lateral spines, which in length exceed half the breadth of the 

 carapace. In section they are nearly round, slightly recurved at 

 their extremities, and taper gradually to a point. The carapace 

 itself measures 1 inch in length and 1| inch in breadth (exclusive 

 of the hepatic spines, which are each 10 lines in length). 



The cardiac region is separated from the branchial regions by two 

 undulating subcentral furrows, and bears a single tubercle upon its 

 centre. The gastric region is ornamented with two small subcentral 

 tubercles. Two prominent equidistant tubercles mark the centre- 

 line of the branchial region, and form, with a third on the meso- 

 gastric region, a prominent ridge on either side the mesial line of 

 the carapace, inclined towards the rostrum at an angle of about 

 80°. A solitary tubercle on the hepatic region, just in front of the 

 base of the great hepatic spine, completes the ornamentation of the 

 surface of the carapace. 



The latero-anterior border appears to have been armed with two 

 or more marginal spines; but the intense hardness of the matrix 

 (a fine-grained quartzite) in which the specimen is imbedded has 

 rendered its development unsuccessful. The posterior border of the 

 carapace is half an inch broad. 



The surface of the carapace (where preserved) shows it to have 

 been very minutely and delicately punctate. 



* From paxts and owfia. 



