RCIIINODERMS OF THE CRAG. 



(prominent) genital and five ocular plates all perforated, and alternating ; one of tlie 

 former combined with a niadrcporiform tubercle ; ambulacral avenues composed of pairs of 

 pores indistinctly ranked ; their ranks confluent throughout. Spines of one order. 



The lu'chins for which I have constituted this genus differ from Tcmnojileurus, to 

 which the best known species has been referred, in having the bosses of the tubercles 

 plain, and not crenulated ; in having no pores at the angles of the plates, and confluent 

 instead of ranked series of sucker-pores throughout the length of their avenues. The last 

 two characters also distinguish them from Microcyphus , as well as (with the first character) 

 from Salmacis. They fill up the inter\'al, in fact, between EcUnm proper and the group 

 of allied genera, with pores, as well as excavations at the angles of their plates. 



It is remarkable that, as yet, no existing sea-urchin can be referred to this genus ; nor 

 are any species recorded from extra- British localities. 



All the known sea-urchins having notched plates are inhabitants of tropical seas, and 

 appear to belong almost exclusively to the Indo-Pacific province. The fossil species of 

 the genera mentioned above are all Tertiary. They belong to Salmacis and Tcmnojjleurus. 

 Two species of the former genus are recorded as European fossils, one from the 

 Nummulitic limestone, and one from the pliocene of Palermo. 



The Temneclmd are remarkable for their beauty, as well as for their rarity. 



1. TjiMNECHiNus ExcAVATUs. Plate I, fig. 1. 



Temxopleurus EXCAVATUS, iS. V. Wood, MS. in Morris, Cat. Brit. Foss., p. GO. 



— WooDii, Ayassiz. Cat. Rais. des Ecliin., in Auu. Sc. Nat., 3d series, 



toiu. vi, p. 3(J0. 

 Temxechinis excavatcs, Forbes. Fig. and Desc. Brit. Org. Rera. Dec. IV, pi. i. 



The general form of this bea\itiful urchin is a depressed melon-shape, hollowed out 

 above. The interambulacral segments are, centro-laterally, twice as broad as the ambu- 

 lacrals ; the sutural pits of their dorsal surface are transversely oblong, very deep, and 

 ccjinpletely confluent, so as to appear like profound undulated furrows with stec]) sides ; 

 centro-laterally, the pits become smaller and disjoined, and decrease gradually in dimen- 

 sions and depth towards the margin of the mouth. The interambulacral plates bear on 

 their elevated ])ortion each a primary tidjercle, seated on a proportionately^ small but 

 prominent smooth boss, and surrounded by granules, those on the dorsal plates being very 

 numerous, and collected on a tumid surface ; those on the ventral being fewer, and inter- 

 spersed among small secondary tubercles, which form rings round the primaries. Of the 

 latter, there are about ten in each half of an interambulacral space, and a like number of 

 sutural pits. The sutural pits of the ambulacral segments are shallow, and partially 

 confluent above. Each ainbidacral ])late bears near its outer or ambulacral margin a 

 primary tubercle, equal in size to those of the interambulacrals, and round this, both 

 dorsally and ventrally, are set secondary tubercles, interspersed with granules. There are 



