234 ECHINONIDtE 



The apical disc is small, and the five ovarial plates are all perforated ; the spongy 

 body is unich rubbed and the ocular plates so blended with the other elements that 

 their individual character cannot be seen. 



The base is covered with the matrix, which adheres so firmly to the test that it is 

 impossible to effect its separation from the surface without at the same time removing 

 the shell. The anatomy of this region is, unfortunately, at present unknown. 



Affinities and Differences. — This species very much resembles Holecti/jms Cenomanensis, 

 Gueranger both in the general outline of the test, the smallness of its tubercles, and in the 

 manner they are disposed on the plates. It is found likewise in nearly the same horizon 

 of the Cretaceous rocks. The only difference I can detect is the presence of the nude 

 ribbon-like bands on the outer side of the poriferous zones, no indication of which is 

 given in M. Cotteau's beautiful and carefully drawn figures. 



Locality and Stratigraplncal Position. — Collected from the Chloritic Marl near 

 Chard, with Catoj)ygus cohimbarius, Pyrina DesmouUnsii, Cottaldia Benettits, and other 

 Upper Greensand forms. 



Family 7. — Collyritid^, d'Orhigny, 1853 (not yet found in British 



Cretaceous strata). 



Family 8. — EcHiNONiDiE, Wright, 1856. 



Test thin, oval ; poriferous zones narrow, meeting at the apical disc ; pores unigeminal ; 

 tubercles of both areas nearly equal in size, but neither perforated nor crenulated ; spines 

 stout, subulate. Mouth-opening nearly central, irregularly pentagonal and edentulous. 

 Vent oblong or pyriform, basal or marginal, closed by anal plates ; apical disc nearly 

 central, four ovarial plates perforated, one imperforate. Ocidars microscopic, tubei'cles 

 small and imperforate. 



The existing forms belong to the genus Echinoneus of Van Phelsum, instituted under 

 the Dutch name Egelschcitze, and adopted by Leske, Lamarck, Deslongchamps, 

 De Blainville, and Desor, to include certain living species of small thin-shelled Urchins, 

 with an oval form and a rounded and inflated border. The ambulacral areas are narrow 

 and lanceolate; the poriferous zones depressed, and the pores small and unigeminal 

 throughout ; the upper surface is flattened, and the apical disc small and excentral ; the 

 two pairs of genital plates are perforated, and the single posterior plate is imperforate ; 

 the base is concave and curved from before backwards ; the mouth-opening small, oblong. 



