ADDENDA. 



ACTINOCRINUS (Saccocrinus) SEMIRADIATUS (n.s.). 



PLATE 10 (1),FIG. 1. 



Body elongate, urn-shaped, slightly constricted near the top of the first 

 radial plates, the sides above being sub-parallel ; base obtusely rounded. 

 Basal plates rather large, forming about one fifth the height of the calyx. 

 First radial plates very large, nearly equalling half the entire height of 

 the calyx, much higher than wide ; second radials small, elongate, hex- 

 agonal ; third radials smaller than the second, wider than high, and 

 variable in form, being mostly heptagonal, supporting on their upper 

 sloping faces supraradials, the number and extent of w^hich are unknown. 

 First interradial plates large, hexagonal, succeeded by two vertical 

 ranges of smaller polygonal plates. Anal area unknown. 

 The specimen from which the above description is taken is an internal 

 cast, imperfect on one side, so that the entire characters are not seen ; but 

 the large size of the first radial plates, and the constriction of the sides 

 above the middle of these plates, is very remarkable. From the characters 

 on the cast it would appear that the plates were marked by rather strong 

 radiating ridges, which, rising from a point above the centres of the first 

 radials, pass to the interradial plates above, while the first radials are 

 smooth below, and in their upper part are marked by sharp rounded 

 ridges, rising from the same point as the oblique ridges, extending upwards 

 and bifurcating with the divisions of the ray as far as preserved in the 

 specimen. 



This feature of narrow rounded ridges, following the divisions of the 

 rays, is approached in some specimens of Saccocrinus christiji == A. whit- 

 fieldi', but the oblique ridges have not been observed, while the entire calyx 

 is much less expanded than in that species. 



Formation and locality. In limestones of the age of the Niagara group, 

 at Racine, Wisconsin. 



RHODOCRINUS [?] RECTUS. 



PLATE X (I), FIG. 2. 

 Crinoajstites ? rectus : Hall, page 318 (14). 

 Having made some careful examinations of the structure of this species. 

 I am induced to believe that it possesses five basal plates, which are 

 shown to be succeeded by five others, holding the place of subradials, 

 and supporting two interradial plates, while the oblique upper faces of 

 the subradials support in succession three radial plates. 



