244 Messrs. R. Etlierkl^-e, Jan., and P. H. Carpenter on 



S. projectus they are verj large, extending through all but 

 the whole length of the caljx. Those of S. Sa>/i\ on the con- 

 trary, are exceedingly short, extending upwards only suffi- 

 ciently far to enclose the distal ends of tlie long ambulacra in 

 their forks or sinuses. • In *S'. (jlaher and 8. missouriensis the 

 radials are again short, but not quite to the same extent as in 

 /8'. Sa>/i, whilst in the former they are much incurved below, 

 to assist in forming the truncate base. The radial sutures are 

 placed in concavities or re-entering angles of the calyx in S. 

 melo^ and, to a certain extent, in S. missouriensis, giving to 

 the entire body a markedly lobate appearance, and to the cross 

 sections a roughly decagonal outline. The oral plates of this 

 genus have no depressed apical tongues more or less divided 

 by a median ridge into two lateral halves, each of which 

 forms the Hoor of a spiracle, as is the case in Pentremites. 

 The size of the orals is naturally in inverse proportion to 

 that of the radial plates. For instance, they are very small in 

 S. melo, S. melonoidesj and S. projectus, and confined quite to 

 the summit. They are comparatively small again in S. pisum, 

 but of medium size in S. glaher and S. granulosus^ and more 

 than one third the length of the body in S. neglcctus. In 8. 

 8ai/ij on the contrary, the orals reach their extreme limit of 

 size, to compensate for the diminished radial plates. This 

 species occupies the same position in 8chizoblastus that G. 

 derhiensis does in Granatocrinus, the relation of the two sets 

 of plates in question affording a very marked point of resem- 

 blance between the two genera. 



The spiracles are oval or linear slits, one on either side of 

 each ambulacrum, but situated at a relatively greater distance 

 from the centre than those of Pentremites. The hydrospire- 

 cleft between the edge of the lancet-plate and the side of the 

 radial sinus is roofed over and converted into a canal by 

 the side plates, the outer faces of which rest against the 

 straight edges of the orals at the proximal ends of the ambu- 

 lacra. These straight edges, however, are not continued right 

 up to the peristome. Some little distance before reaching it 

 they bend inwards towards one another, and then curve out- 

 wards again before converging towards one another at the 

 apex of the plate. At these points, therefore, the hydrospire- 

 clefts are slightly wider than at the more distal parts of the 

 ambulacra ; and as the latter decrease in width the side plates 

 fail to fill up the gap between the lancet-plate and the orals, 

 which is thus left open as a spiracle, and is not closed by the 

 summit-plates when these are present. The spiracles of 

 8c]uzuhlastus, speaking generally, are much more outside the 

 orals than those of Pentremites. It is well shown in 8. 8ai/i, 



