807 



Cew^/s— COLLYRITES,* Behc, 1S31; DesmouUns, 1835. 



Disaster, Agassiz, 1836. 

 Disaster, Besor, 18-12. 

 CoLLYKiTES, cYOfhujny, 1853. 

 CoLLYRiTES, BesoT (pars), 1857. 



The generic characters of this group have been already indicated in our description 

 of the family of which it is the type. The CoUyrites, in general, are urchins of moderate 

 size, although some species attain a considerable magnitude. They have an ovoid, oblong, 

 cordiform, or triangular shape, more or less depressed on the dorsal surface, and have the 

 anterior border slightly grooved, with an anteal sulcus, in which the single area is lodged. 

 The ambulacral areas are disjoined, and form two distinct summits on the dorsal surface ; 

 the anterior, composed of the single area and anterior pair, occupies the anterior third of 

 the dorsal surface ; and the posterior, composed of the posterior pair, meet over the vent 

 near the posterior third. The poriferous zones are narrow, equal, and complete ; the pores 

 unigeminal, the holes round, oval, or oblong; and the zones visible throughout from 

 the mouth to the summits. 



The apical disc, situated at the anterior summit, at the junction of the three anterior 

 ambulacra, is composed of four perforated genital plates, between which are interposed 

 two large, ocular plates. The right antero-lateral genital plate is the largest, and supports 

 a prominent, spongy, madreporiform body ; the anterior ocular is a very small plate, which 

 is lodged between the anterior genitals. The two posterior ocular plates are seen only in 

 well-preserved specimens at the apices of the posterior ambulacra. 



The mouth-opening is situated in the anterior third of the base; the peristome 

 is obtusely pentagonal, approaching a circular form. 



The oval or elliptical anal opening is situated in the middle of the posterior 

 border, and is in general destitute of a distinct anal area, and always without a fasciole. 



The tubercles are small, uniform in size, and are perforated and crenulated ; the miliary 

 granules are small and numerous. 



The first known species of this genus were placed by systematic authors in different 

 genera, with which they had few characters in common. Leske grouped them with the 

 Spatangites, Lamarck with the Anancliyies, Defrance, Goldfuss, and Miinster, with the 

 Nudeolites. In 1831, M. Deluc, in a letter to M. Desmoulius,t proposed for the urchin 

 which Lamarck named Ananchytes elliptica, that of CoUyrites sub-ellipticay but it was not 

 until August, 1835, that M. Desmoulins estabhshed definitely the genus Collyrites.\ 



* From the Greek Collyra, a little loaf. 



f Desmoulins ' Etudes sur les Echinides,' ler Memoire, p. A7 . 



X Desmoulins, loc. cic, p. 46. 



