in some Fossil Eclrinoidea. 261 



the manner of distribution of the pore-pairs. They are triserial, in 

 the order a, b, c ; but, while the pairs of b and c follow the outline of the 

 phyllode more or less definitely, series a passes in a straight line, 

 from, the point where expansion of the ambulacrum begins, to the 

 corners of the ambulacral margin of the peristome. Thus, in the 

 widest part of the phyllode, these pore-pairs are distinctly separate 

 from the marginal series. They exhibit no difference in size or 

 proportion from the outer pairs. 



Clypeus hugi, Agassiz. PI. XIII, Fig. 6. Inferior Oolite. 



The phyllodes of this species differ from those of the last only in 

 their greater expansion. The plating is as nearly identical with that 

 in C. ploti as can be expected, and the isolation of the central series 

 («) of pores is no more complete since the peristomial margins of the 

 ambulacra are proportionately wider. 



Pygurus michelint, Cotteau. PI. XIII, Fig. 8. Great Oolite. 



The genus Pygurus shows the development of the floscelle in 

 a considerably advanced stage. The prominent bourrelets and broad 

 concave phyllodes give a very beautiful appearance to the adoral 

 surface in all the species of the genus. On the adapical surface the 

 ambulacra are broadly petaloid, but are uniformly composed of 

 primaries. Xo plate-crushing appears until the broadening of the 

 phyllode commences. The result is structurally very similar to that 

 in Clypeus, but in the course of their passage across the very wide 

 ambulacra the plates undergo a modification which seems to have an 

 important significance when the structure of the next form ( Catopygus) 

 is considered. Plate c hardly ever becomes an actual demiplate, but is 

 connected to. the perradial suture by a very narrow band. Similarly, 

 plate a is rarely quite separated from the interradial margin. Its 

 perradial portion is expanded in such a way that, besides reducing the 

 vertical diameter of plate c to a very small amount, it exerts a 

 considerable crushing influence on plate b, which thus becomes narrow 

 perradially and proportionately broad interradially. In this way the 

 perradial suture comes to be formed of the edges of plates of series a 

 more than of those of b and c combined, while these latter series make 

 up almost the entire interradial margin. 



Catopygus carinatcs, Leske. PI. XIII, Fig. 9. Cretaceous. 



The phyllodes in this species are the most complex in structure of 

 any that I have seen. Unfortunately the small size of the specimens 

 renders the tracing of the plate - outlines peculiarly difficult. The 

 figure given is, after the manner of a composite photograph, generalized 

 from a series of camera-lucida drawings taken from all five phyllodes 

 in some nine or ten specimens. It may be further mentioned, in 

 support of the figure's accuracy, that it was made before I had 

 adequately studied the simpler types of phyllode, and so is the 

 product of an unbiassed mind. The ambulacra are only slightly 

 sub-petaloid on the adapical surface, so that Cotteau's assertion that 

 complex phyllodes and broad petals are always associated does not 

 apply to this case. The bourrelets are but slightly prominent, and 



