1881.] NATURAL SCIENCES OF PHILADELPHIA. 391 



appendage, which are paved with a great number of small 

 irregular polygonal plates. It is not at all improbable that these 

 areffi were susceptible of a certain amount of contraction and 

 expansion, and that the}' performed an important function in 

 connection with the tubular extensions, in the introduction and 

 expulsion of water. 



Generic Diagnosis. — Body generally large, subglobose, about 

 equilaterally pentamerous ; plates of the calyx convex to nodose 

 or spiniferous ; base concave, vault flat, its margins extended 

 into five free tubular appendages, situated between, or partly 

 above the rays. 



Underbasals five, small, pentagonal, forming a flat impressed 

 pentagon, entirely involved in the basal concavity, and some- 

 times hidden by the column. Basals five, hexagonal or obtusely 

 heptagonal, truncate above, and like the first radials often 

 produced into sharp spines, which extend obliquelj^ downward 

 Primary' radials 3X5, the first larger than the rest, heptagonal, 

 the second hexagonal, the third hexagonal or heptagonal and 

 supporting on its upper sloping sides the secondary radials, in 

 two series of two to three plates each, which' diverge rapidly, 

 arching over the interradial spaces, and completel}^ separating them 

 from the vault. The last secondaiy radial supports the small 

 delicate arms, its inner sloping side being indented by the arm 

 opening, while its outer side bears an additional plate, which 

 meets with a similar plate of the adjoining ray, and the two 

 together form the base of a false arm. 



Interradial and anal areae scarcely distinguishable from each 

 other; large, oval, sometimes slightly depressed. They are 

 occupied b}^ from ten to eighteen pieces, of which there is one 

 large hexagonal plate in the first range, resting on the truncate 

 upper side of the basals, and between two first radials. This is 

 succeeded by from three to five ranges, the second, third and 

 fourth consisting of three — rarely four — plates, and those above 

 of two and one plate. Interaxillary plates two to eight or ten, 

 the upper ones connecting with the vault and the false arms. 



Arms four to nine to the ray, according to the species, the 

 number of primary arms being perhaps restricted to four, 

 the additional ones being produced by branching very close to 

 the body. They are slender and delicate, composed of a double 

 series of interlocking plates, and they bear minute pinnules 



