PALEOPNEUSTES CRISTATUS. 15 



of the test somewhat conical ; posterior extremity arching somewhat less 

 from the apex to the anal system, which is placed in the truncated extremity, 

 slightly concave towards the anterior of the posterior interambulacral space. 

 The sides of the test rise nearly vertically from the ambitus, curving slightly 

 as far as the extremity of the petals, where the test slopes more rapidly to 

 the apical system. Seen from above the outline is elliptical, rounded ante- 

 riorly, with slightly angular sides ; posterior interambulacrum somewhat 

 pointed, rounded, projecting beyond the general outline. Actinostome an- 

 terior, sunken, with test sloping rapidly towards it from the anterior ex- 

 tremity. Actinal surface flat, with shar2:)ly rounded ambitus. Posterior lip 

 of actinostome prominent ; actinal plastron slightly sloping from the central 

 line towards the bare, broad, posterior, lateral ambulacral avenues ; the whole 

 actinal surfoce, with the exception of the ambulacra, covered by large 

 tubercles, uniformly scattered, and comparatively (to the abactinal surface) 

 crowded with distant miliaries ; in the intervening spaces the miliaries alone 

 extend over the bare posterior ambulacral avenues, while in the lateral 

 anterior ambulacra, close to the actinostome, adjoining the large actinal 

 suckers, small secondary tubercles are found. 



The imperfectly petaloid portion of the lateral ambulacra consists of a 

 large interior round pore, with a large exterior comma-shaped pore. The 

 interporiferous zone becomes gradually broader towards the extremity of 

 the petals ; it is smooth, and is flanked by the poriferous zone, which is as 

 broad as the median space, and attains its greatest breadth quite near the 

 apical system. The petals of the lateral ambulacra extend about half-way to 

 the ambitus ; the posterior pair are somewhat the longest. Below the petals 

 the poriferous zone consists of minute pairs of pores, placed in the centre of 

 the plates, extending to the ambitus ; they are larger on the actinal side, 

 and form a very marked phyllode in the ambulacra round the actinostome. 

 The petaloid portion of the lateral ambulacra is slightly sunken near the 

 apical system, and becomes flush with the test at the extremity of the petals. 

 The odd ambulacrum is flush with the test, and wholly composed of minute, 

 distant pairs of pores, placed in the central part of the ambulaci'al plates, as 

 in the lower part of the lateral ambulacra. 



On the abactinal surface the tubercles are uniformly scattered, distant, 

 arranged irregularly in short, curving lines, on the central part of the plates, 

 leaving the edges of the j^lates bare, forming thus bare median interambu- 

 lacral and ambulacral sutural spaces, as well as bare, horizontal sutural mar- 



