GENERA AND GROUPS OF THE ECHINOIDEA. 89 



" en marsupium " in tlie females. This is not quite capable of veri- 

 fication ; but it bas nevertheless originated the name of a genus, 

 Tliylechinus. 



G-enus Thtlechinus, Pomel, 1883, Theses, Glass. Meth. p. 91. 



Lamlert, 1888, Hxtr. Bull. Soc. d. Sci. Nat. de V Tonne, p. 11. 



(Amended.) 

 Sjn. Cypliosoma (pars), Cott., Per. et Gautb. 1881, Eeb. Eoss. 

 de I'Alger. fasc. 8, p. 172, pi. xix. figs. 3-10 {Cyphosoma 

 Said). 



Test with a compact symmetrical apical system ; radial plates 

 excluded. 



Ambulacral plates having three components and three pairs of 

 pores in simple series only. Pairs of pores uniserial throughout; 

 the interporiferous areas with two vertical rows of crenulated 

 tubercles smaller than those of the interradia. 



Interradia witb two vertical rows of large primary tubercles 

 crenulated. The median areas more or less depressed dorsally. 



Peristome large ; lips unequal ; branchial incisions slight. 



Fossil. Cretaceous : Europe, N. Africa. 



Por the generic position of CypTiosoma Seinzi, Per. et G-auth., 

 see p. 83, 



Division II. 



The genus Micropsis, Cotteau, 1855-56, was diagnosed so as to 

 include M. JDesori, which has four vertical rows of ambulacral 

 tubercles, and the pairs of pores in arcs of four ; the interradial 

 plates very wide and rather low, with a primary tubercle and 

 three small primaries on one side, and two on the other on each 

 plate. There is no doubling of pairs, and the branchial incisions 

 are small ; but the number of coronal plates is great. It is like 

 a Coptosoma with a considerable number of coronal plates. 



A species, Micropsis microstoma, has three vertical rows of 

 tubercles and five or six pairs of pores in arcs, to a plate. Again, 

 M. Leymerii has only two pairs of vertical rows of tubercles and 

 three pairs of pores to a plate. All the radial plates enter the 

 apical ring. We do not understand how M. glohosa, Cott., and 

 M. leridensis, Cott., can be associated with the type species in 

 the same genus. The Micropsis we described from the Nummu- 

 litic of Sind has many of the characters of, but the structure of 

 the ambulacra differs from, M. Cotteau's type. 



