152 CLASS IV. 
principally, if not exclusively, of marine plants (Fuci, Conferve) ; 
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 Kunin, 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, Micraster, 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 Drissus AGASS. 
we note: 
Spatang. ventricosus, Rumpu. Amb. Rariteitk. Tab. xiv. No.1; this 
foreign species attains a very large size. To the proper genus Spatangus 
AGASS. belongs Spat. purpureus, Buainv., Actinol. Pl. xiv., Forprs Brit. 
Starf. p. 182, in the North Sea and Mediterranean. The form is heart- 
shaped, Of this species MinnE Epwarps has given an anatomical figure 
in Cuvier Rk. Anim. éd. illustrée, Zoophytes, Pl. xt. bis. See also some 
notices on the Anatomy of Spatangus in ScuwEraceEr’s Handb. der Natur- 
geschichte der skelettl. vingeglied. Thiere, s. 538, 539. 
The mouth is in this genus without teeth. There are only four 
ovaria or testes present, as also only four port 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 Ericuson’s Archiv f. Naturgesch., 1845, s. 344, 
&c. Tab. Xt. ; 
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 Bronen. Deser. géol. des environs de Paris in 
Cuvier Rech. s, 1. ossem. foss. 1. 2 Pl. v. fig. 7, Bronn Leth. géogn. Tab. 29, 
