724 
PEOEESSOE WYYILLE THOMSON ON THE ECHINOIDEA OE THE 
fenestrated structure, indicating its modification into the madreporic tubercle. A large 
definite round aperture, about one third of the width of the plate from its outer edge, is 
in connexion with the duct of the ovary. The “ ocular plates ” are heart-shaped, with 
a well-marked opening for the lodgment of the sense-organ. The plates of the periproct 
are irregular in form, diminishing in size towards the central anal opening ; five of the 
outer row, however, are somewhat spear- or lancet-shaped, and pass outwards between 
the inner angles of the ovarial plates, giving the periproct a stellate form. The central 
portions of the ovarial, the ocular, and the larger anal plates bear close-set granules, but 
round the edge the plates are smooth and bare. This smooth border round the indi- 
vidual plates of the apical disk is a style of ornament very characteristic of this species, 
although not special to it. 
The oral opening of the corona is 25 millims. in diameter. The peristome is markedly 
pentagonal. The buccal membrane is closely covered with thick and strong imbricated 
scales, their free edges beset with granules for the articulation of spines and pedicellarise. 
The pairs of pores which traverse the ambulacral scales are smaller, and have the pores 
more closely set than those of the pore- are se of the corona. The jaw-pyramid is of the 
ordinary form. The epiphyses of the jaw-sockets are rather longer and more developed 
than those of the more typical species, such as C. tribuloides, and the rotulse are longer 
and rather more slender. The teeth are strong and sharp, formed of a simple deeply 
grooved band of semitransparent, very dense calcified areolar tissue. The auriculae are 
large and spade-shaped ; they arise entirely from the interambulacral plates ; they 
lean slightly over the ambulacra, but they form no approach to an arch. The plates 
supporting the walls of the ovaries are large and closely set (Plate LIX. figs. 12, 13) ; 
they appear to originate from calcareous spicules with three rays spreading in one plane, 
the open angles between the branches becoming gradually filled up with thin cribriform 
calcareous expansions. The plates imbedding the wall of the intestine (fig. 11) and 
those in the suspending folds of the mesentery (fig. 10) are small and irregular in shape. 
The external tube feet, which are similar in character throughout the entire length of 
the ambulacra, have their walls supported by long curved spicules, rough with small 
conical projections ; they terminate in sucking-disks, whose skeleton consists of a very 
irregular rosette of four, five, or six wedge-shaped pieces (Plate LIX. fig. 8 ). 
The primary spines or radioles articulated to the primary tubercles on the inter- 
ambulacral plates are large ; those round the ambitus of large spines are sometimes 
150 millims. in length by 6 or 7 millims. in greatest diameter. They are slightly 
enlarged just beyond the neck, and taper very gradually, rarely in full-grown spines 
coming to a point, but usually ending abruptly with a kind of cicatrix, which sometimes 
takes the form of an irregular cup. The surface of the spine is finely granular, and 
usually from twelve to fourteen rows of small pointed tubercles rather than spines, 
pointing slightly outwards, traverse its entire length at equal distances ; sometimes these 
tubercles become regularly spine-like, and project from a continuous raised crest; and 
sometimes, as in a very marked variety dredged by Count Pourtales in the Gulf-stream 
