BRITISH FOSSILS. 



9 



18. D. tumidum, Forbes, 1. c. 



Circular, inflated ; lat. 9, alt. 5 lines ; ambulacra straight ; tubercles numerous, small, 

 subequal, those of each division in 2 distinct rows ; areolae small, slightly radiated ; 

 ambulacral tubercles separated by a double row of granules ; interambulacrals bordered 

 by a few very small accessory tubercles ; interspaces granulated, becoming quite bare near 

 the apical opening. (Spines slender, solid, smooth. Coll. Bowerbank.) 



Locality/. — Chalk Marl of Dover. Chlor. marl. Somerset. (Coll. Wright ; Tennant.) 

 The original specimen was presented to the Museum of the Geol. Survey by Edwd. 

 Clarke, Esq., and stated to be from the Gault of Folkestone. It is partly incrusted 

 Avith pyrites, and filled with a matrix of what appears to be Grey Chalk. A 

 better example of the same species in the Brit. Museum, undoubtedly from the 

 Grey Chalk of Dover, has 12 or 13 tubercles in each row. 



19. Z). Carteri, Woodw. 



Circular, tumid ; lat. 10, alt. 6 lines ; pairs of pores in single file ; ambulacral tubercles as 

 large as the interambulacral at the circumference, becoming much smaller above and below, 

 in 2 close rows of 11 each, alternating ; interambulacral tubercles 12 in a row, separated 

 by a moderately wide granulated space, and flanked by rows of about 6 secondary 

 tubercles externally, on the under side. Base concave ; apical opening small. 



Closely related to D. tumidum, Forbes. The ambulacral bosses are closer together, 



and the secondary rows of interambulacral tubercles more developed. 

 Locality. — Upper Green Sand, Cambridge. (Coll. L. Barrett, and of Jas. Carter, 

 Esqrs. 



Section B. Primary interambulacral tubercles in 4 rows ; pores in double series at the 

 summit. {Tetra gramma, Agassiz.) 



20. I>. variolare, Alex. Brongniart, 18-34, Env. Par. p. 152. pi. M. f. 9. {sec. Forbes.) 

 Syn. Cyphosoma Milleri, Forbes, in Dixon, Geol. Sussex, pi. 25. f. 17. (Mus. 



Bowerbank.) 



Localities. — Specimens agreeing pretty well with M. Agassiz's published cast occur 

 in the Chalk Marl of Dover (Brit. Mus. and Mus. Pract. Geol.), but it is im- 

 possible to ascertain what species was intended by M. Brongniart's figure and 

 description, without reference to the original specimen. 



It is rather singular that in Morris's Catalogue (p. 77.), we are referred for a re- 

 presentation of this species to Agassiz's figure of D. Brongniarti, whilst Bronn 

 (Index, p. 1261.) and D'Orbigny (Prodrome, 2, p. 142.) quote Brongniart's 

 figure of D. variolare in illustration of Agassiz's D. Brongniarti. Bronn also 

 quotes Goldfuss's Cidarites variolaris, which is a Cyphosoma, and D'Orbigny places 

 both species in the Gault, 



21. D. Brongniarti, Ag., Ech. Suiss., t. 14. f. 4—6. 



Localities. — Grey Chalk, Dover (Brit. Mus.). Chloritic Marl, Maiden Bradley, 

 Somerset (Geol. Survey). These specimens have been compared with typical 

 examples from the Upper Green Sand of the Perte du Rhone. In the recently 

 published Synopsis of M. Desor, this species is accidentally placed in the genus 

 " Pseudodiadema,'" amongst the species with pores in single file, whilst D. variolare 

 is placed in the genus Diplopodia. 



22. D. Mackiei, n. sp. 



Inflated, depressed; lat. 24 lines; oral opening deeply sunk, lat. 6 lines; apical opening 

 pentagonal, 7\ lines ; ambulacral pores crowded above ; prunary tubercles not diminishing 

 sensibly above, but decreasing regularly below ; ambulacral tubercles in two rows of 17 

 each, at wide intervals above, the rows separated by a continuous granulated space ; 

 interambulacral tubercles in 6 principal rows, bordered at the circumference by accessory 



