CARDIASTER. 293 



The extinct genera are 



Echinocorys, Breynius. Holaster, Agassiz. 



Stenonia, Desor. Cardiaster, Forbes. 



All the extinct genera are found in British rocks with the exception of Stenonia, 

 which is collected only in the White Chalk of Italy, or Scaglia of the Vicentin, at 

 Monte di Magre. The living genus Pa^eopneustes, Agassiz, has at present an 

 "incertum sedis " in this group. 



Genus — Cardiaster, Forbes, 1850. 



Spatangus, Auctorum. 

 Holaster (pars), Agassiz. 

 Infulaster, Borchards. 



Test cordate, tumid, or depressed ; lateral ambulacra having the upper part of their 

 avenues slightly dissimilar ; all the ambulacra convergent on the vertex, the anterior 

 single ambulacrum lodged in a strongly marked anteal sulcus with angulated borders. 

 A fasciole passing beneath the vent and continued on the sides. Apical disc elongated, 

 and composed of four perforated genital and five perforated ocular plates. Tubercles 

 perforated, raised upon crenulated bosses, and surrounded by areolae. 



Cardiaster possesses all the characters of Holaster, from which it is distinguished 

 by the presence of a subanal fasciole, and a deeper anteal sulcus with more angulated 

 sides. 



Cardiaster Benstedi, Forbes, 1852. Pl.'LXVI, figs. 3 a, b, c; PI. LXXI, figs. 4 and 5. 



Cardiaster Benstedi, Forbes. Mem. of Geol. Survey, decade iv, pi. ix, notes, 1852. 

 — — Morris. Catalogue Brit. Foss., 2nd edit., p. 73, 1854. 



Diagnosis. — Test cordiform, broad, hemispherical, upper surface convex, rotund, 

 anteal sulcus shallow, lateral ambulacra narrow, poriferous zones narrow and unequal. 



Dimensions. — Length one inch and a half; breadth one inch and a half; height one 

 inch. 



Description. — The anteal sulcus is strongly marked and wide below. The upper surface 

 is gently curved, convex, and rotund. The poriferous zones are all remarkably narrow, 

 and the posterior as broad as the anterolaterals. PI. LXVI, fig. 3 a, represents the upper 

 convex surface, showing the very narrow zones with the central apical disc and its four 



