236 On a new Genus of Spatangoids. 



In Python Sebce. the fluctuation of this vein between the 

 single and double condition was more plainly seen. Just in 

 front of the gall-bladder the vessel communicates with the 

 gastric portal vein ; from this point to two inches behind the 

 gall-bladder it is single. For a distance of 4^ inches it is 

 formed of two tubes lying side by side ; these then reunite and 

 finally again separate to form two tubes. This example 

 shows that the double character of the vein is not only due 

 to the elongation of the body, and as a consequence the 

 equivalent of the posterior double region of the same vein in 

 Lacertilia, where it emerges from the two posteriorly situated 

 fat-bodies. 



XXV. — Description of a new Genus of Spatangoids. 

 By F. Jeffrey Bell, M.'A. 



Among the Prymnodesmid Spatangoids (or those with a 

 subanal fasciole) the genera known as Brissus, Meoma, and 

 Metalia are ordinarily recognized as forming a compact 

 group. I have lately received from a valued correspondent, 

 Mr. F. W. Townsend, some specimens from the coast of 

 Oman which have a striking resemblance to these three, but 

 are at once distinguished from all of them by the position of 

 the apex, which is hardly, if at all, excentric. This sub- 

 central position of the apex suggests that this new form is 

 phvlogenetically older than the three genera to which it seems 

 to be allied; and I suggest for it, therefore, the name of 

 Eobrissus. 



The genus may be diagnosed in the following term? : — A 

 Prymnodesmid Spatangoid with the apex almost central and 

 the anterior ambulacrum flush with the test ; the antero- 

 lateral ambulacra directed forwards and not at right angles 

 to the long axis of the test ; an open circumanal fasciole, as 

 in Metalia. 



The possession of a circumanal fasciole has generally been 

 regarded as a recent acquisition, so that it is of importance to 

 note its coexistence with the archaic position of the apex. 



Specific characters and name. — As there is but a single 

 form known, the specific characters must be guessed at. In 

 general appearance like a small Brissus unicolor, with light- 

 coloured Brissine spines, none of much greater length than 

 the rest ; those on the abactinal side longer and sharper than 

 those on the actinal. Larger tubercles scattered among the 

 smaller on the actinal surface, more regularly larger below ; 

 the lateral ambulacra moderately wide and slightly sunken. 

 Four pairs of pores on each side within the subanal fasciole. 



