ilE. J. AV. GREGORY ON ARCH^OPNEUSTES ABRUPTUS. 163 



15. Archj20pnefstes abrtjptus, a I^ew Genus and Species of 

 EcHiNoiD from the Oceanic Series in Barbados. By J. W. 

 Gregory, Esq., B.Sc, P.G.S. (Eead January 6tli, 1892). 



[Plate IV.] 



Contents. 



Page 



I. Diagnosis of the Echinoid 163 



II. Zoological Affinities 164 



III. Geological Evidence , 168 



I. Diagnosis OF the Echinoid. 



Arclueoptieustes, nov. gen."^ — Test large, elongate; high and 

 generally conical, with the anterior slope much the steepest. 

 Anterior ambulacrum flush. 



Apical system : ethmolysian (in cases which are certainly known ; 

 but M. Cotteau's figure leaves the matter doubtful in one species). 



Ambulacra : the 'lateral are subpetaloid, broad and unequal ; the 

 petaloid portions extend to the ambitus. The pores are large ; in 

 the posterior pair the outer pores are elongate or comma -shaped. 

 The anterior ambulacrum is reduced, and contains only very small, 

 scattered, single pores. 



Peristome : very excentric anteriorly. Labiate : in a depression. 



Periproct : on the narrow posterior vertical margin. 



Fascicles : none, or possibly an imperfectly developed marginal 

 one. 



Distribution. — Cainozoic (recent and fossil) in West Indies. 



Species 1. (Type of genus) Archceopneustes hystria? (A. Agassiz). 



Species 2. Archceopneustes ahruptus,~ u. sp. 



Eorm : anterior margin well rounded and with no anterior 

 groove ; the maximum width, which, is greater than the length, is 

 at a little less than a third of the length of the test from the 

 anterior margin ; from the widest part the sides taper back by a long 

 curve to the narrow posterior end. Seen from the sides the anterior 

 margin is short and steep ; and from the vertex there is a long 

 backward slope which increases in steepness till it reaches the 

 posterior margin. 



Apical system : at the apex, very excentric anteriorly ; details 

 unknown, but it is probably compact. 



Ambulacra : the antero-lateral pair diverge from the apex almost 

 at right angles to the long axis of the test ; the postero-lateral are 

 longer and broader. Both pairs are flush ; the inner pores are 



1 The name is due to the characters being more archaic than in the case of 

 its nearest ally, Falceopneustes. 



- The specific name refers to the abruptness of the anterior slope. 



