96 Dr. T. Wright sn a new Genus of Fossil Cidaridae, 



apical disc more largely developed, and in the species being nearly 

 all small and depressed forms, Hemipedina is related to Echin- 

 opsis in possessing uncrenulated and perforated tubercles, with 

 the pores in pairs ; but it is distinguished from the latter by the 

 narrowness of the ambulacral areas, the depressed form of the 

 test [Echinopsis being high and inflated), the form of the mouth- 

 opening, and the deep decagonal lobes of the peristome (that of 

 Echinopsis being almost deprived of these incisions), together 

 with the greater size and development of the elements of the 

 apical disc. 



Hemipedina, as far as we at present know, is composed of 

 Jurassic species, which commence in the lower Lias and extend 

 into the Coral Rag, each stage possessing its own specific forms. 

 The following synopsis of the British species now before us will 

 be figured and described in detail in our Monograph on the 

 British Oolitic Cidaridse. 



A. Species from the Lias. 



Hemipedina Bechei, Wright. 



Cidaris Bechei, Broderip, Geol. Proc. ii. 202. 



Diadema Bechei, Agassiz, Morris's Catalogue of British Fossils, 

 1st ed. p. 51. 



Test small, much crushed, and covered over with spines ; ambu- 

 lacra with two rows of tubercles; interambulacra with four 

 or six rows of tubercles ; spines long, slender and needle- 

 shaped, Y^o^hs of an inch in length, with longitudinal lines on 

 the surface. This appears to be identical with the type-spe- 

 cimen in the Museum of the Geological Society. 



Locality. — Lower Lias, Lyme Regis. 

 Coll. J. S. Bowerbank, Esq. 



Hemipedina Bowerhankiiy Wright, no v. sp. 



Test crushed, 1 2 ^th of an inch in diameter ; ambulacral areas nar- 

 row, with two rows of marginal tubercles rather smaller than 

 those in the interambulacra, a tubercle on every alternate 

 plate ; interambulacral areas wide, with six rows of tubercles 

 abreast, surrounded by a delicate scrobicular circle; spines 

 shorter and thicker (l^^ths of an inch in length) than those of 

 H. Bechei, although the test is much larger, deeply sculptured 

 with longitudinal lines. 



Locality. — Lower Lias, Lyme Regis. 

 Coll. J. S. Bowerbank, Esq. 



