ECHINOIDEA. 21 



chain. This will be more convincing if we compare the ratio height to length 

 of some of the specimens. Arranged in ascending order, these figures are : 



•60 -61 '68 71 -72 -73 "80 -81 -83 -86 -92. 



We have therefore at one end specimens where the height is barely '6 of the 

 length, while at the other end there are forms where it reaches more than '9, yet 

 both these extremes are connected by a series of intermediate forms which are some- 

 times difficult to classify. I have arranged them in such a way that var. penta- 

 SrowaZis includes all the forms of which the ratio is below 0*63; var. tumida 

 includes all those below '80 and var. glohosa all those above '80. 



The above arrangement seems to represent the three varieties very well, but if 

 we sort a number of specimens, there will always be some specimens having 

 a ratio '64 or '81, which it is difficult to include amongst the one or the other 

 variety, between which they form the connecting links. However, such speci- 

 mens must be expected and they only prove that, though there is a large 

 difference between a specimen of the ratio '60 and one of the ratio '92, it is im- 

 possible to consider them different species. 



The varieties as above described, may be referred to Fyrina ataxensis, Cotteau, 

 although it seems that the species from Baluchistdn become sometimes more penta- 

 gonal in plan and globular in shape than the specimens figured on plate 988 of the 

 Paldontologie fran9aise ; on the other hand, the var. tumida agrees so well in shape 

 with Cotteau's species, that I have not hesitated to identify the Baluchistan 

 £orms with it. 



Pteina gugantea, spec. nov. PI. IV. fig. 6-6c. 



Dimensions. 



Length L . ..........=: 61 mm. 



Breadth b = 44 „ 



Height h = 38 „ 



i =•«« 



L ='* 



The test has a subpentagonal shape, being slightly broader anteriorly than 

 posteriorly ; the upper surface is highly inflated, conical ; the profile is much 

 more sharply curved on the anterior side, than on the posterior one, where it slopes 

 more gently. The sides are rounded, the lower surface is slightly pulvinated, only 

 around the peristome it is a little depressed. 



The apical disc is small, slightly excentral in an anterior direction ; the four 

 genital plates are rather small and perforated by large holes, but the madrepore 

 plate surpasses the others considerably in size and completely fills the centre. The 

 ocular plates are minute and hardly visible. 



The ambulacral areas are narrowly lanceolate, extending from the apical disc 

 to the peristome ; the poriferous zones are linear, very narrow, and slightly concave. 

 The minute pores are equally rounded and arranged in oblique pairs, which on the 



