112 Dr. T. Wright on Fossil Echinoderms 



and pentagonal, with a deep sulcus extending from the angles 

 to the border, and corresponding to the middle suture of the 

 ambulacral areas : anus small, round, and submarginal : 

 granulations larger and more prominent at the base than on 

 the dorsal surface. 



Description, — This beautiful Clypeaster has been so long known, 

 that it seems unnecessary to give any lengthy details of its struc- 

 ture ; although it jnay be remarked, however, that we are not 

 aware that a detailed description of the species exists. It was 

 first introduced to notice through the figure of Scilla, and the 

 specimens before us belong to the same type as that given in his 

 work. Many of the Maltese varieties of this species, however, 

 are remarkable for their deviation from this typical form ; the 

 dorsal surface in them rises into a campanulate shape, and 

 the circumference becomes almost round. These varieties con- 

 stitute the Clypeaster turritus, Agass., from the Miocene of 

 Dax, and the Clypeaster Agassizii, Sismonda, from beds of the 

 same age near Nice. We have before us a similar conical 

 variety from Malta, belonging to the Museum of the Bristol 

 Institution ; and others, collected by the Marchioness of Hast- 

 ings, are in the Jermyn Street Museum. 



All the specimens in Earl Ducie's cabinet, with one exception, 

 belong to what we regard as the typical form. This remark- 

 able exceptional specimen agrees with the brief notice of C. 

 yflwncMS*, Desor: — "Tres grande espece, allongee, pentagonale, 

 k bord fortement renfle. Zones poriferes tres large k leur ex- 

 tremite. Tert. du Taurus, ile de Crete." If we are correct in 

 referring all these varieties to C. alius, it follows that this species 

 has a wide range of deviation from what we take to be its typical 

 form ; but these limits of variation are probably not greater in 

 this than in some other species of Urchins. The following 

 table shows the relative dimensions of three forms, — the typical, 

 the conical, and the flattened and tumid varieties : — 



The ambulacral areas are largely petaloid, nearly equal in 

 length and width ; they are rounded, widely open below, 

 and extend over four-fifths of the dorsal surface in the type 

 form, over nearly three-fourths in the conical form, and over 

 almost four-fifths in the tumid varieties ; in all, the areas form 



* Cat. raisonne des Echinides, Ann. Sc. Nat. torn. vii. p. 131. 



