70 THE FOSSIL ECHINOIDEA 



rectly given by MM. d'Archiac and Haime, and it is found that the diagnosis, 

 although remarkably clear, is hardly positive enough, and yet too comparative, especially 

 as it relates to two other genera from which this is distinguished. 



Genus EURHODIA, d'Archiac and Haime (amended). 



The test is large and stout; it is elongate, oval, and is truncated posteriorly, 

 broad in front, depressed, rather flat, or slightly rounded above, slightly concave 

 actirally and tumid at the ambitus. Apical system and rosette small, eccentric in front ; 

 petals small, unequal, open, especially that of the odd ambulacrum. Poriferous zones 

 unequal in size. Peristome large, eccentric in front, very elongate longitudinally, 

 pentagonal ; floscelle highly developed ; pitted structure in the median line of the test 

 inferiorly. 



Periproct elongate transversely, supramarginal, transverse, in a shallow broad 

 groove, which shelves backwards and is surmounted by a rounded roof. 



1. EuEHODiA MoEEisii, d'ArcMac and Haime. Plate XVIII, Figs. 1-7. 



Pygorhynchus Morrisii, d'ArcJiiac, 1850, ffist. des progris de la Geol. t. iii. p. 248. 



The thick test is long, rather depressed, ovoid at the tumid margin, broad in front, 

 widest in front of the centre, on a line with the peristome, and tapering backwards 

 to a posterior truncated edge. The apical surface is highest behind the centre and 

 between the posterior ambulacra ; it slopes slightly on a comparatively plane surface to 

 near the end of the odd ambulacrum, and then merges into the boldly convex ante- 

 rior portion of the test, which unites with the tumid margin. Behind, the slope is 

 more sudden, and there is a rounded low keel, which reaches backwards along a slope 

 very much less defined than the anterior convexity of the test, and which reaches to 

 the edge over the supramarginal periproct. The keel and the test slope on either side 

 lapidly to the sides of the test, so that this part is less tumid and narrower than the 

 anterior portions. The posterior edge of the test is rounded, but is rather sharp ; it is 

 nearly straight transversely, but just a little incurved, and the broad shallow periproct- 

 groove slopes upwards and forwards from it. The actinal surface is nearly flat, but 

 there is a longitudinal and central depression, at the anterior end of which is the 

 peristome ; posteriorly the actinal surface is very slightly produced downwards. 



The apical system is small and eccentric in front ; there are four generative 

 pores, and the madreporic is central ; the outer pores are well developed. The ante- 

 rior odd ambulacrum is straight, open, and the outer series of pores of the poriferous 

 zones curves to the straight inner series. The interporiferous zone is broader than one 

 of the poriferous zones. The pores of this and of the other ambulacra are conjugate, 

 and the outer series are more elongate than the inner, which often are circular in 

 outline ; the pores of a pair are more widely spaced in the middle of the poriferous 

 zone than at the extremities; and sometimes the conjugation is difficult to trace in 

 the middle of the zone in some specimens. The pores of all the ambulacra are 



