152 CLASS IV. 



principally, if not exclusively, of marine plants (Fuel, Confervce); 

 according to others it would seem to live on Molluscs, but the 

 fragments of shell, often found with considerable quantity of sand 

 in the intestinal canal, may have been contained in the sea-water 

 swallowed, and need not by any means to be looked on as the 

 remains of shell-fish that had been consumed. 



Petrified shells of Sea-urchins are found in great numbers in 

 secondary strata, particularly in the chalk-formation, the interior 

 being usually filled with silicious earth. 



* Anus eccentric superior or inferior, 

 a) Mouth eccentric. (Genital pores 4.) Spatangoidea AGASS. 



Spatangus KLEIN, LAM. Ambulacra circumscript, five or only 

 four, the odd one (the anterior) being either little distinct or 

 wanting. Test ovate or cordate, often at the fore-part furnished 

 with a furrow proceeding from the summit. 



Genera Holaster, Hemipneustes, Micr aster, Spatangus, Amphi- 

 detus, Brissus, Schizaster AGASSIZ. 



Some species of this division are fossil, and occur especially 

 in the chalk-formation, others in tertiary deposits. Amongst the 

 species now living, which chiefly belong to the genus Brissus AGASS. 

 we note : 



Spatang. ventricosus, RUMPH. Amb. Rariteitk. Tab. xiv. No. i ; this 

 foreign species attains a very large size. To the proper genus Spatangus 

 AGASS. belongs Spat, purpureus, BLAINV., Actinol. PI. xiv., FOKBES Brit. 

 Starf. p. 182, in the North Sea and Mediterranean. The form is heart- 

 shaped. Of this species MILNE EDWARDS has given an anatomical figure 

 in CUVIEB R. Anim. 3d. illustree, Zoophytes, PI. xi. bis. See also some 

 notices on the Anatomy of Spatangus in SCHWEIGGER'S Handb. der Natur- 

 geschicJite der skelettl. ungeglied. Thiere, s. 538, 539. 



The mouth is in this genus without teeth. There are only four 

 ovaria or testes present, as also only four pori genitales. PHILIPPI 

 not long ago described three American species in which only three 

 genital pores existed, and which he united under the name of 

 Tripylus. See ERICHSON'S Archiv f. Naturgesch., 1845, s. 344, 

 <kc. Tab. xi. 



Ananchytes LAM. (exclusive of some species), AGASS. Ambu- 

 lacra radiating and diverging from the vertex to the margin, not 

 interrupted. Body irregular, oval or conoid ; test without a furrow 

 to the anterior ambulacrum. 



Sp. Ananchytes ovata Cuv. and BRONGN. Descr. geol. des environs de Paris in 

 CUVIER Rech. s. 1. assent, foss. 11. 2 PI. v. fig. 7, BRONN Leth. geogn. Tab. 29, 



