aEliTEEA AND Q-EOTJPS OP THE ECHINOIDEA. 225 



Genus Faorina. 



Pericosmus. 



Linthia. 



Schizaster. 



Prenaster. 



Ornithaster. 



Coraster. 



Agassizia. 



Moira. 

 Subgenus Moiropsis. 

 Genus Hypsopatagus, 



Tlie genus Semiaster, Desor, has been greatly modified of late 

 years, and some proposed new genera, which are characterized by 

 peculiarities in the apical system alone, have been shown to be 

 of no value (Ann. & Mag. Nat. Hist. ser. 6, 1888, vol. ii. p. 329). 

 Desor took no notice of the apical system in his first definition, 

 but unfortunately restricted the genus, subsequently, to the 

 species which had an ethmophract system, the madreporite being 

 in the right anterior basal plate. Loven, A. Agassiz, and Gau- 

 thier have, however, explained the variability of the position of 

 the madreporite and of the number of basal plates and genital 

 pores. The classification adopted lately by M. Pomel, M. Munier- 

 Chalmas, and by M. Cotteau is not consistent with the researches 

 of zoologists. 



The following is the first definition of the genus Semiaster : — 



Genus Hemtaster, Desor, 1847, Catal. Rais., Ann d. Sci. Nat. ser. 3, 

 vol. viii. p. 16, fig. in vol. vi. pi. 16. fig. 7- 

 Small swollen urchins; ambulacral summit posterior; ambulacra in broad 

 shallow grooves, the posterior shorter than the anterior pairs. Peripe- 

 talous fascicle angular, encircling the ambulacral star ; no subanal fasciole. 

 Differs from Micraster in its more swollen shape and the fasciole. 



Desor divided the genus : — 1 type, Posterior ambulacra very 

 short and barely half the length of the anterior petals. 2 type, 

 Posterior ambulacra almost as long as the anterior, divergent, 

 petals. 



In Desor's Synopsis, 1858, p. 367, the following diagaosis 

 occurs : — 



" Small, squat, short tests, swollen above and at the sides, trun- 

 cated behind, a shallow anterior groove; apical system compact, 



LINN. JOTIEN. — ZOOLO&T, VOL. XXIII. 15 



