Oct., 1907. New Crixoids — Slocom. 283 



height of the calyx. Radials five, equal, sides slightly converging 

 towards the base; moderately convex longitudinally, so that the ven- 

 tral view of the calyx is subpentangular. A semicircular excavation 

 occupies nearly the entire distal edge of the radials, and the processes 

 thus formed are rather short for the genus. The costals are not pre- 

 served in the type or any of the specimens at hand. The inter- 

 radials or orals are large and are not visible in a side view; they 

 comprise the greater part of the ventral disc. They extend to the top 

 of the radial processes, and rest against their inner faces. Laterally 

 they connect with each other, but leave a comparatively large round 

 opening for the peristome in the center of the disc. The deflected 

 lateral edges form the ambulacral groove extending from the arm 

 bases to the central opening. The anal opening is situated at the 

 juncture of the posterior interradial with the processes of the two 

 posterior radials. None of the plates which covered the peristome, 

 ambulacral grooves or anal opening is preserved. 



The natural casts are similar in form to the exteriors, but slightly 

 constricted at the arm bases and somewhat shorter in proportion to 

 their diameter. The interradial processes are indicated by five rather 

 stout protuberances between which the dorsal cup curves gradually 

 into the convex ventral disc. A large circular protuberance in the 

 center of the disc indicates the size and position of the peristome, and 

 a small one rising out of the posterior interradial process indicates the 

 anal opening. 



Dimensions of the type are as follows: 



Natural mold Natural cast 



Height of calyx, 6.7 mm. Height of calyx, 4.5 mm. 



Height of basals, 3.3 " Height of basals, 1.3 " 



Height of radials, 2.4 " Height of radials, 2.4 " 



Height of processes, 1.0 " Height of processes, 0.8 " 



Diameter at arm bases, 5.0 " Diameter at arm bases, 2.9 " 

 Diameter at top of basals, 4. 1 " Diameter at top of basals, 3.0 " 

 As to size, form and pattern of ornamentation, this species ap- 

 proaches 5. hammelli S. A. M. * and from the original description and 

 figures it would hardly be safe to separate them. Upon comparison, 

 however, with the types of S. hammelli, which are in the paleontological 

 collections of the University of Chicago, the ornamentation of the 

 plates was found to be so much more prominent in the specimens here 

 described as to warrant specific distinction. The striations in both 

 species are so grouped as to form geometric figures. For instance, the 

 longitudinal striae on the right posterior radial and the basal on which 

 * 17th Rept. Geol. Ind., p. 635, PI. VI, Figs. 7-9. 



