DESCRIPTIONS OF THE sl'l-CII-s. 225 



dded, en a level with the general surface of the calyz ; Lancet-plates partially 

 exposed throughout nearly their entire length, and perforated by three canals, 

 arranged in a triangle; ambulacra! groove broad and shallow, side plates aboul 

 eighty 1 , transversely wedge-shaped ; outer side plates small and apparently triangular. 

 Hydrospire-tubes four on each side, much convoluted; bydrospire-canals large and 



expanded below. Spiracles ten, small linear slits, notching the edge8 of the deltoids; 

 posterior spiracles not continent with the anus, but protected like it by the hood-like 

 central end of the anal deltoid. Mouth small; summit-plates minute and penta- 

 gonal. Ornament of the radial plates consists of strong festoon-like granular ridges, 

 parallel to the outline of the plates ; the obtuse sides and central ridge of the 

 deltoids are also granular, and the surface contiguous to and parallel with the radio- 

 deltoid sutures bears several V-shaped obtuse ridges. 



Remarks. Schizoblastus Sayi \s readily distinguished from S. melonoides (PL VI. 

 fig. 10), and from all the doubtful American species in the list which we have given 

 above — with the exception of Pentrermtes Potteri, Hambach — by the very large size of 

 its deltoid plates, which form almost the whole of the calyx, as in Elaiacrimcs (PL II. 

 fig. 46). In this respect, however, it resembles the Irish Schizoblastus Rofei (PI. VIII. 

 figs. 9, 10) ; but this type has a simple anal spiracle, with nothing like the great hood 

 projecting above the three openings which is so characteristic of S. Sayi. There 

 seems to be something of the kind in Granatocrinus negleetus, M. & W,, which has. 

 much smaller deltoids than S. Sayi and a protuberant base, but in the absence of 

 specimens we cannot say whether it is a Schizoblastus or a Cryptoblas/us. 



According to Shumard, there are about eighty side plates in the ambulacrum of 

 S. Sayi, but we have not been able to count more than fifty on each side. 



The shape of the calyx seems to vary a good deal, two varieties being clearly distin- 

 guishable. One is almost globose, and is not unlike some forms of Granatocrinus 

 orbicularis (PL IX. fig. 11); while the other is more elongated, and resembles one 

 variety of G. ellipticus (PL VIII. fig. 19). A similar variation occurs in G. Nbrwoodi 

 (PL II. figs. 32-35). 



Schizoblastus Sayi is of interest as being one of the first species which were found 

 to have the peristome covered by summit-plates. Shumard - gave a good figure illus- 

 trating this point, and another has since been published by Wachsmuth and Springer 3 , 

 while it is also shown in our PL III. figs. 2, 3. Hambach 4 , however, altogether 



1 Fide Shumard. 



- " Palaeontology " in Swallow's First and Second Ann. Report Geol. Survey, Missouri. 1855, pi. li, 

 fig. 1 e. 



3 'Revision of the Paheocrinoidea,' Fart II. 1881, pi. xix. fig. 3. There is an unfortunate error in this 

 figure, the deltoids being represented as small plates within the circle of spiracles. Hambach has made 

 use of this as an argument against the existence of the summit-plates, which are also represented in the 

 figure. 



4 Trans. St. Louis Aead. Sci. 1884, vol. iv. no. 3, p. 540. 



2g 



