FROM TPIE UPPER GREENSAND. 255 



The apical disc is nearly central, with four perforated ovarials and five small oculars, 

 the spongy body extending into the middle of the disc. 



The mouth-opening is nearly central, always obliquely elongated. 



This genus belongs essentially to the Cretaceous formations. The Upper Greensand, 

 Craie Chloritee, or Etage Cenomanien, has yielded C. trirjonopi/ffus, faba, rostratus, and 

 orbicularis ; of these the first three are found both in the Anglo-Parisian and in the 

 Pyrenean basins,, and the last up to the present time only in the Anglo-Parisian basin. 



In the White Chalk, or I'Etage Senonien are four species — C. avcllanus, sidcato-radiatus, 

 tniiicatus, ?iw^ peltiformis, all of whicli are found in the Anglo-Parisian basin. 



The only specimen discovered in England is C. rostratus. 



Caratomus rostratus, Ayassiz, 1840, PI. LVII, fig. 2 a — e. 



Caratomus kosteatus, Agassiz. Catalogus Syst. Ectyp., p. 7, 1840. 



— — Besor. Monog. des Galerites, p. 38, pi. 5, figs. 1 — 4, 1842. 



— — Morris. Cat. of Brit. Foss., p. 49, 1843. 



— — Agassiz et Desor. Cat. Rais., p. 93, Modele No. 81, 1847. 



— — d'Orbigny. Prodrom., t. ii, p. 178, Stage 20e, 1847. 



— — Forbes. In Morris' Cat. of Brit. Foss., p. 73, 1854. 



— — (/'Or%Ky. Pal. Fran9aise, Ter. Cre'taces, pl.941,p. 367, 1855, 



Diagnosis. — Test thick, depressed, round, inclining to oblong, obtusely round before, 

 and prolonged into a rostrum behind ; apical disc slightly excentral ; base convex, 

 pulvinated, depressed near the, mouth, wdiich is small, oblique, and excentral; vent 

 triangular, infra-rostral at the lower third of the height ; ambulacra narrow and obscured 

 by large scrobiculated tubercles. 



Dimensions. — Antero-posterior diameter four tenths of an inch ; breadth three tenths 

 of an inch ; height two tenths of an inch. 



Description. — This little Urchin was first figured and described by M. Desor in his 

 beautiful Monograph on the Galerites and has since been figured by d'Orbigny in the 

 ' Paleontologie Eran9aise.' The shell is thick and depressed, longer than wide, very obtuse 

 anteriorly, and ending in a prolonged rostrum posteriorly, which gives it a pyriform 

 aspect. 



The ambulacra are narrow and scarcely visible, being obscured by large scrobiculated 

 tubercles ; in order to expose the poriferous zones it is often necessary to treat the 

 test with some dilute acid. I have never been fortunate enough to obtain so good a 

 specimen as the one which my late esteemed friend Mr. Bone procured for his beautiful 



