126 ECHINODERMA. ECHINOIDEA 



a large primary perforated tubercle which bears a long spine. 

 Peristomal membrane covered with plates. Carboniferous Lime- 

 stone. Ex. A. urii. 



Fig. 51. Melonechinusmultiporus, Carboniferous. Part of an ambulacral 

 area (a) and an interambulacral area (b) from the equator of the 

 test. Based on figures given by Jackson, x 2. 



Cidaris. Test spheroidal, the summit and base equally flat- 

 tened. Apical disc very large, rarely preserved fossil, ocular plates 

 large. Ambulacra narrow, flexuous, plates simple, pores unigeminal ; 

 between the rows of pores are vertical rows of small tubercles and 

 granules. Interambulacra wide, plates large, each with a primary 

 tubercle which is perforated, and may be crenulated or smooth ; 

 areola large, surrounded by secondary tubercles, beyond which may 

 be granules. Peristome rounded, its membrane covered with plates. 

 Spines large, of various forms, generally ornamented with rows of 

 granules. The term Cidaris is here used in the extended sense, and 

 really includes several genera. Jurassic to present day ; allied 

 forms occur in the Trias. Ex. C. florigemma, Corallian and 

 Kimeridgian. 



Peltastes (fig. 47 A). Test circular in outline, depressed. 

 Apical disc very large, prominent, containing one extra plate, the 

 sur-anal, placed in front of the periproct ; the madreporic plate 

 has an oblique fissure. Ambulacra narrow, straight or slightly 

 flexuous, with small tubercles ; pores unigeminal except near the 

 peristome ; ambulacral plates, simple primaries. Interambulacra 

 wide, with large primary tubercles, which are imperforate, but may 

 be crenulate. Peristome slightly notched. Upper Jurassic to 

 Gault. Ex. P. wrighti, Lower Cretaceous. 



Salenia. Similar to Peltastes, but the periproct is placed to 

 the right of a median line drawn from the anterior to the posterior 



