60 



MESOZOIC llADIATA. 



Diplopodia (M'Coy), n. g. 

 Gen. Char. Depressed, subpentagonal from the pro- 

 jection of the ambulacral spaces; two rows of 

 primary tubercles both on the ambulacral and 

 interambulacral spaces ; ambulacral rows of two 

 pairs of pores in the upper half, of one pair in 

 the middle and becoming again compound, of 

 two or sometimes three pairs of pores towards 

 the mouth. 



This genus is distinguished from Diadema, to 

 which it is most allied, and Pedina, by the former 

 having uniformly one pair of pores in a row% and the 

 latter having uniformly three pairs of pores in a row. 

 The following species and the D. subangulare (Ag.) 

 are the types of the genus, which is only known in Ambulacrum 



the oolites. «f Diplopodia. 



Diplopodia pentagona (M^Coy). 



Sp. Char. Pentagonal, depressed, having an average diameter of 

 9 lines, with a height of 4 lines ; interambulacral spaces one- 

 third wider than the ambulacral at middle ; two distinct rows 

 of primary tubercles in each interambulacral space, surrounded 

 by few small granules, and having on the outer side near the 

 mouth five or six secondary tubercles one-third the size of the 

 primary, forming a short single irregular row scarcely reaching 

 the middle ; ambulacral spaces with two rows of primary tu- 

 bercles nearly equalling those of the interambuiacra in size, 

 having a few crowded granules between the rows but no se- 

 condary tubercles ; there are only five or six pairs of ambu- 

 lacral pores disposed in the single part of the row, rather be- 

 low the middle, above which the pairs of pores are in regular 

 double rows, each pair being separated by a diagonal line; 

 below the single part of the ambulacra the pairs are in irre- 

 gular double series increasing to three rows near the mouth. 



This differs from the Diadema (Diplopodia) subangulare (Ag.) 

 in its more depressed and distinctly pentagonal form, in the very 

 short single portion of the ambulacra, there being nineteen or 

 twenty pairs of pores in a single vertical row in the middle of 

 that species, and in the deficiency of secondary tubercles along 

 the margin of the interambuiacra. 



Not uncommon in the great oolite of Minchinhampton. 



[Col. University of Cambridge.) 



Discoidea marginalis (M'Coy). 

 Sp. Char. Nearly circular, dcj)resscd (length and width 1 inch. 



