2 



BRITISH FOSSILS. 



peculiar mineralized condition similar to that exhibited by examples 

 from cretaceous beds near Biarritz, which, judging from a specimen 

 communicated by Mr. Pratt, seem to be very closely allied to if 

 not identical with Cardiaster granulosus. 



The outline of this elegant fossil is regularly cordate. In front 

 it is deeply furrowed by the sulcus for the odd ambulacrum, which 

 excavation has angulated but sloping margins. Behind it is obtusely 

 truncate. The general form is expanded, usually as broad as long. 

 The back is depressed, the apical disk nearly central, the hinder 

 interambulacral segment gently arched and declining, the vent 

 placed low, the margins of the body rounded yet somewhat com- 

 pressed, the base flattened yet slightly convex, the mouth close to 

 the anteal margin and at the extremity of the deep groove, that 

 terminates the odd ambulacral furrow. The test varies in degree 

 of convexity and expansion, but on the whole is very constant in 

 form. All the dorsal plates are thickly covered with minute 

 granules interspersed with tubercles, the latter consisting of a 

 perforated knob placed on a crenulated boss, and surrounded by a 

 smooth areola. These tubercles are very unequal. On the anterior 

 interambulacral spaces, but confined to their inner halves, are two 

 rows of tubercles much larger than any of the others. A similar 

 series of large tubercles runs along the carinated portion of the 

 posterior interambulacral area, above the vent. On the under 

 surface the tubercles are thickly grouped and moderately large, 

 especially near the sides, and on the lanceolate post-oral spinous 

 space ; but there are only granules on the two broad avenues 

 formed by the inferior continuations of the posteal ambulacra, or on 

 the central portion of tlie anteal ambulacrum. 



In the dorsal portion of the odd ambulacrum the avenues of 

 pores are homogeneous throughout, the pores of each pair are placed 

 close together, and the pairs become more distant as the plates 

 become larger. There are about 28 plates visible in a well grown 

 example. The antero-lateral ambulacra are sub-petaloid in their 

 upper part, and unsymmetrical in consequence of the pores of each 

 pair being wider apart in the outer row than in the inner, and 

 moreover being united by a deeper groove. There are about 24 

 pairs of pores in the broader or subpetaloid portion of each series, 

 they are closely approximated, and those that are below widen out ; 

 the outer series is slightly arcuated. In the postero-lateral 

 ambulacra the two series are nearly similar, and there are about 

 18 pairs of pores in the upper or subpetaloid portion of each series. 

 There are about 9 plates in each series in the dorsal portion of the 



