10 THE FOSSIL ECHINOIDEA 



On examination, however, it is found to differ from Echinolampas in so many points 

 that we feel compelled to regard it as the type of a new genus. 



Plesiolampas differs from Echinolampas in its almost straight ambulacra, its 

 subequal poriferous zones, its round, nearly equal pores, its periproct placed longi- 

 tudinally, its mouth, and the absence of a definite floscelle, and, lastly, its imperforate 

 tubercles. 



The large longitudinal periproct of Plesiolampas recalls Amblypygus, from which, 

 however, the present genus is easily distinguished by the form of the test, the characters 

 of the ambulacra (above mentioned), the single pores on the ambulacral plates of the 

 actinal surface, and the character of the peristome, which in the new form is sub- 

 pentagonal or transversely elongate and certainly not oblique. 



No other Cassidulid appears to approach sufficiently near to need comparison. 



This genus is also represented in the Eanikot series above the Trap in Sind. 



1. Plesiolampas eloi^gata, sp. nov. Plate I, Figs. 8-16. 



General form elongate, depressed, convex above, tumid at the sides and in front, 

 slightly rostrated behind. Actinal surface sunken round the peristome, otherwise convex. 

 Marginal contour nearly elliptical, rather more rapidly tapering behind than in front, 

 and also slightly truncate. The longitudinal profile shows the apical summit to be 

 slightly excentric in front, and more so than the peristome ; the posterior slope is very 

 gradual until it reaches the margin, where it is roundly curved over the posterior 

 rostration ; the anterior slope is much more rapid, and the rounding of the upper 

 portion of the margin less bombous. The transverse profile shows the dorsal area to be 

 evenly rounded, not conoid ; and the lateral slopes are more rapid than either of the 

 slopes of the longitudinal profile. 



The apical system corresponds with the apical summit of the test, the distance 

 from the centre of the system to the anterior margin being about 40 per cent, of the 

 length. 



There are four generative pores, which are large ; the anterior pair round, and the 

 posterior pair elongate and subpyriform and larger than the anterior pores. The 

 ocular plates and pores are exceedingly small. The madreporiform body occupies the 

 whole of the centre of the system. 



The ambulacra are narrow, straight, flush with the surface of the test, widely open, 

 and do not reach the margin, the posterior pair being the most remote from it. The 

 postero-lateral ambulacra are rather longer than the antero-laterals ; but these latter 

 are perhaps slightly broader, and the odd anterior ambulacrum is a shade narrower 

 than either of the others. The anterior pair form an angle of 135° with one another, 

 and the posterior pair an angle of 61°, this latter being the index of the odd posterior 

 interradium. The shape of the odd anterior ambulacrum and of the posterior pair is 

 that of a straight narrow band, converging regularly and somewhat rapidly to the small 

 extremity at the apical pole ; and their breadth, at the widely open extremity, is only the 

 slighest degree narrower than the breadth at the widest portion across the middle of 



