THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY 



[SECOND SERIES.] 

 No. 46. OCTOBER 1851. 



XXI. — On the Cidaridse of the Oolites, with a description of some 

 new species of that family. By Thomas Wright, M.D. &c* 



[With three Plates.] 



The Echinoderms form the highest class of the radiated animals ; 

 it includes organisms which are either fixed or free, composed of 

 a regular but very complicated skeleton, secreted by and inclosed 

 within organized membranes, and often preserved in admirable 

 perfection in the fossiliferous strata of all periods of the earth's 

 history. The study of this class, although hitherto much neg- 

 lected by geologists, presents many points of importance to the 

 progress of their science, for the test of Echinoderms exhibits 

 characters of more import and significance than those afforded 

 by the shells of Mollusca. Unlike the testaceous covering of that 

 class, the test of Echinoderms constitutes an internal and inte- 

 gral part of the animal, participating in its life, intimately con- 

 nected with the organs of digestion, respiration and generation, 

 as well as with those of locomotion and vision, and having in 

 consequence many of the distinctive characters of the organism 

 impressed upon it. 



In all Echinoderms, the external parts of the body, with the 

 organs of locomotion, are disposed around a common centre ; in 

 the spherical forms they are arranged in rows like the lines of 

 longitude on a terrestrial globe, and the mouth and the anus are 

 situated at the opposite poles : the elements of the body are re- 

 peated several times in the composition of the skeleton. 



It has been shown by M. Agassizf that the radiated type of 



* Read at Cheltenham at the Meeting of the Cotteswold Naturalists' 

 Club, June 24, 1851. 



t Prodrome d'une Monogr. des Echin,, Mem. Soc. de Neuchatel, torn. i. 

 p. 168. 



Ann. % Mag. N. Hist. Ser. 2. Vol. ym. 16 



