34 LARVIFORM CRIXOIDS 



vault. Although the sutures between the plates can not be made out with 

 certainty the plates are probably arranged as follows: (1) a low and small 

 infrabasal disc; (2) a ring of five rather short irregular and somewhat un- 

 equally sized basal plates; (3) five stunted radial plates that do not meet 

 laterally ; and (4) a comparatively large inflated vault composed of five oral 

 plates. 



Although the details of the basal disc can not be determined it is un- 

 doubtedly low and saucer shaped and its lower part slopes steeply downward 

 to the circular stem facet. 



The basal plates are probably rather irregularly sub-hexagonal in out- 

 line and of somewhat different size. The proportion of height to width varies 

 but the dimensions are approximately the same. The height of these plates 

 differs however with the result that the little radial plates stand at varying 

 distances above the base of the calyx. 



The radials are very small. Near the middle of the upper edge of each 

 occurs a small triangular drooping lip which is interpreted as an arm facet. 

 The arms must have been very small. No articular processes have been 

 observed in connection with these nor are openings into the interior of the 

 calyx visible. 



The anal opening is situated slightly below the level of the right posterior 

 arm facet and much nearer this than the left posterior facet. It is very small 

 but rendered conspicuous by a curved outstanding lip which occurs beneath it. 



The oral vault makes up by far the greater part of the calyx. The 

 individual plates are of approximately equal size and shape except that the 

 posterior oral is somewhat wider than the others. As they slope gently out- 

 ward from the center of the ventral surface the oral plates become broadly 

 concave between their somewhat upraised edges which meet and form five 

 broadly rounded radiating ridges. As the orals curve sharply downward to 

 form the upper part of the sides of the calyx their median concave depres- 

 sions persist but their edges probably produced sharp angular vertical ribs 

 strongly developed to a positon only a short distance above the arm facets. 

 These vertical ribs have been broken off from the holotype however and ap- 

 pear in this specimen as narrow slits leading into the interior of the calyx. 



The surface of the holotype. which is silicified, is rather rough probably 

 indicating that the plates were originally minutely porous. 



Remarks. — This species closely resembles certain abnormal specimens 

 of Cranocrinus figured by Wanner [17, pi. 1, figs. 10. 11 |. but its association 

 with Tytthocrinus comptus, described below, is evidence that it is actually 

 the normal representative of a type intermediate between Cranocrinus and 

 Tenagocrinus. 



