CONTRIBUTIONS TO PALEONTOLOGY. 129 



Anal area larger than the interradial, and occupied by a greater 

 number of plates; not limited above by a single summit-arm like 

 those, but opening to the dome, and having a more slender sum- 

 mit arm arising from each side : these arms are composed of four 

 ranges of small plates, tlie range on the lower side largest. This 

 arrangement gives six summit-arms, instead of five as in the other 

 species of this genus. 



Surface of plates finely granulose. 



The first and second radials bear on their centres long spines. The 

 plates of the radial series are elevated above the arms, giving (in 

 a basal view) a pentalobate form to the body. Summit composed 

 of numerous very small plates, and ornamented by several lo- 

 zenge shaped depressions as in the typical forms of the genus. 



The lateral or true arms, in this species, present some differences of 

 structure and mode of attachment from those observed in one of the 

 typical species of the genus. The arm-plates originate on the second 

 supraradial, and are alternately wider on one side. Each arm bifurcates 

 on the fifth plate above its origin, and continues undivided as far as the 

 eighth plate above this, having the character of the arms of Cyathocrinus 

 or PoTERiocRiNus; while those observed in the Carboniferous species ap- 

 pear like slender and pendulous tentacula. Better specimens of the latter, 

 however, are required to determine these characters in detail. 



Geological formation and locality. Shales of the Hamilton group : On- 

 tario county. 0. A. White, collector. 



GENUS ACTINOCRINUS (Miller). 



ACTINOCRINUS NYSSA ( n. s.). 



Calyx hemispherical, with a tripartite rim surrounding the base, 

 formed by the projection of the lower margin of the basal plates. 

 Column-cicatrix of moderate size, scarcely depressed. First radial 

 plates of medium size, the upper and lower lateral faces subequal. 

 Second radials a little smaller than the first, somewhat regularly 

 hexagonal. Third radials smaller than the second, heptagonal, 

 supporting still smaller hexagonal supraradials on the upper 

 margins : these again support a brachial plate, with a single arm 

 on the outer face and a secondary supraradial on the inner face : 

 this again supports a brachial and single arm on the inner face, 

 and a series of three supraradials of the third order on the outer 

 face, the upper one of these supporting an arm on each side; 

 giving four arms to each main division of the ray, or eight arms 

 to each ray = 40 arms. 

 [Senate, No. 116.] 17 



