ECHINOCYAMUS. 9 



its congeners, that it must be regarded as distinct. The form is a depressed, but not 

 lobed spheroid. The genital disk is less prominent, and smaller, than in the other species 

 of the genus. The genital plates seem to have been decorated by fewer tubercles. The 

 ambulacral segments are half the breadth of the interambulacral divisions. The sutural 

 pits are defined, rather small, and not confluent. The primary tubercles on both ambu- 

 lacral and interambulacral are much larger than in the other Temnechini, and surrounded 

 by wider areolae. There are about ten interambulacral, and thirteen, or so, ambulacral 

 tubercles in a vertical row. The pores are arranged as usual. The specimen described 

 measures half an inch across by rather more than a quarter of an inch in height. 



In Mr. Morris's 'Catalogue of British Fossils,' a Salenia is mentioned as occurring, on 

 the authority of Mr. Searles Wood, in the Coralline Crag of Sutton. The specimen 

 alluded to has been submitted to my examination, and proves to be an immature sea- 

 urchin, apparently the fry of one of the species of Temnechinus. The plates of the genital 

 disk exhibit an appearance of pitting and rugosity which is anomalous, and strongly 

 resembles at first glance the sculpture of the plates of Salenia. Hence the mistake about 

 its generic position. There is, however, no supplementary plate, as in that genus. The 

 traces of pits at the angles of the plate distinctly indicate its affinities with Temnechinus. 

 Otherwise it might, with its large disk, have been considered a young Goniopygus. 



Family. — Clypeasterid.e. 



The urchins of this family are more or less rounded, often ovate, generally depressed. 

 Their shells are thick, and frequently strengthened within by calcareous buttresses. Their 

 mouths are central ; their vents eccentric. They are provided with a dental apparatus of 

 more simple structure than that characteristic of the Echinida. Their ambulacra are either 

 distinctly petaloid and convergent, or, as in the examples about to be described, are sub- 

 parallel. They have five genital and five ocular plates, but these are not all perforate in 

 every case. The species found in the Crag are, with doubtful exceptions, all of the 

 same genus with the representative of the family in the British Seas at present. 



Genus — Echinocyamus, Von Phelsum. 



Body depressed, ovate or sub-orbicular, with ambulacra which are sub-heterogeneous, 

 their dorsal portions forming pseudo-petals with nearly parallel or slightly diverging 

 avenues. Test thick, and strengthened within by ribs ; its surface covered with small and 

 similar tubercles, which bear rather short slender spines. Mouth round, and sub-central 

 or central. Vent inferior. Four genital pores. A dental apparatus arming the 

 mouth. 



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