Clypeus. RADIATA. ANOCYSTI. 479 



Avenues of the pores nearly smooth, and narrower than the preceding. 

 The double row of primary tubercles in each compartment very^distinct, the 

 smaller ones few in number, having a space hi tho middle of each, nearly 

 smooth. 



* Five double rows of pores in each avenue. The ring round 

 the vent formed by the plates qf the pelvis and the costals. 



4. E. subangularis. — Each oblique row of pores curved to- 

 wards the mouth, the intervening spaces with a row of tuber- 

 cles. 



Cidaris subangularis, Leske, p. 106. t. iii. C, D.— Common on the rocks 

 with E. eseulentus. 



In each of the large compartments there are about ten tubercles in each 

 transverse row, and in the smaller about six. Each plate, however, has one 

 tubercle larger than the rest. The margin of each pair of pores seems raised, 

 with a groove between those which are contiguous in the same row. The 

 markings on the avenues of pores appear to distinguish this species from the 

 Rupestris of Leske, p. 111., which is the Saxatilis of Gmelin. It is probable 

 that this species has been confounded with E. esculentus. The structure of 

 the pelvis, and the number of pores, characters belonging to different sys- 

 tems of organs in the animal, leave no room to doubt of the propriety of their 

 separation. 



EXTINCT SPECIES. 



1. E. saxatilis. — Hemispherical, depressed ; compartments with two rows of 



small, nearly equal tubercles ; little more than half an inch in diameter. 



Park. Org. Rem. iii. t. iii. f. 1 — Mant. Geol. 189 Chalk. 



2. E. Konigii — Circular, much depressed, lesser compartments with two 

 rows of tubercles ; thirty rows of tubercles on the vertex, and twenty on the 

 base Park. Org. Rem. iii. 12. t. i. f. 10 — Mant. Geol. 189 Chalk. 



Gen. CLYPEUS. — Depressed, with ten avenues of pores in 

 pairs ; a groove from the vertex to the margin on one side. 



1. C. sinuatus. — Round, the avenues of pores, in the pairs, recede from each 

 other from the vortex towards the margin — (Plot, t. ii. f. 9, 10.) — List. An. 

 Ang. 224.— Park. Org. Rem. ii. t. ii. f. 1. — Oolite. 



2. C. lobatus — The groove deep, and dividing the margin into two lobes— 

 List. An. Ang. 223 — Oolite. 



3. C. clunicularis.-m Oval— (Smi/A's Fossils, f. 6.), Geol. Eng. 188. — Oolite. 



PLEUROCYSTI. 



Gen. III. ECHINARACHNIUS.— Mouth central. 



5. E. placenta. — Subconic, with five avenues of pores, cir- 

 cumference angular, base flat. 



Echinus p. Linn. Syst. mcv. 16— "Isle of Foulah, very rare," Professor 

 Jameson. 



