296 CARDIASTER 



latissimus, Agassiz, so well figured in the ' Paleontologie Erancaise.' A careful 

 comparison of the two fine specimens before me, which formed the subjects of our plate, 

 with three specimens of C. orbicularis from the Etage Cenomanien de Cap-le-Heve, shows 

 that Cardiaster latissimus is more depressed and proportionately wider to its length than 

 the specimens of C. suborbicularis from Havre measured by me. Moreover, in the 

 latter the under surface is more convex, and the plastron ridged, and the posterior border 

 more elevated than in our English specimen. I have lately had the advantage of 

 examining at Auxerre my friend Monsieur G. Cotteau's magnificent collection of recent 

 and fossil Echinodermata, and of comparing Cardiaster orbicularis and C. latissimus with 

 each other, and find that his type-specimens of the latter species are identical with the 

 Echinide I have figured under that name from the Upper Greensand of Dorsetshire. 



The body is cordiform and much depressed, it is rounded before, and deeply grooved 

 by the anteal sulcus, the sides are widely expanded, and the posterior border is 

 contracted and acuminated. The upper surface is convex and a little more elevated at 

 the anterior than at the posterior third ; a ridge rising along the middle line from the 

 disc backwards gives a marked character to the smaller specimen (figs. 2 b and c). The 

 pairs of ambulacra are unequal. The anterior pair are slightly curved outwards and 

 forwards, and the posterior are shorter and directed straight outwards and backwards 

 (figs. 1, 2 b). The poriferous zones are narrow, and composed of small equal-sized 

 holes (fig. 2 e). The anterior single area is lodged in a deep sulcus, the zones are feebly 

 developed, and the holes very minute (fig. 2/). The surface of the plates, especially 

 those about the anterior border and the base, has a number of small tubercles developed 

 on their surface (figs. 2 a and 2 e). The tubercles are mammillated, with crenulated 

 bosses and perforated summits (fig. 2y). The apical disc is small and elongated, with 

 four perforated ovarial plates (fig. 2 h) and five small oculars. 



The under surface (fig. 2 a) is flattened, a little convex in the region of the plastron, 

 and concave at the sides and around the anterior border. The mouth-opening is placed 

 in a depression near the junction of the anterior fourth with the middle fourths of the 

 base. The peristome is small and bilabiate (fig. 2 a). The arrangement of the tubercles 

 on the base is very well shown in this drawing, which gives a more correct notion of 

 their comparative size and distribution than any description can convey. 



The vent is situated high up in the posterior border (fig. 2 c), which is narrow and 

 truncated obliquely downwards and inwards (fig. 2 b), with a beak-like process 

 overhanging the upper angle of the vent, the periprocte of which has an oval form 

 (fig. 2 c). 



Affinities and Differences. — I have already pointed out the affinities and differences 

 subsisting between this species and C. suborbicularis; there is no other congeneric 

 form in our Upper Greensand strata with which it can be confused ; it is altogether a 

 very rare form in our area. 



Locality and Stratigraphical Position. — The large specimen was obtained from the 



