250 



arm-plates, six rows to cacli ray, of which the inner i-ows of tertiary 

 plates each support two and the outer one ; so that there are thirty 

 arms, which are robust and fringed with stout pinnulre. The arm- 

 pieces are first single and sub-cuneiform, but change gradually until 

 about the fifth or sixth plate they consist of two rows of interlocking 

 and alternating cuneiform plates. 



In each interradial area the proximal series consists of one plate, 

 resting directly on one of the basals, succeeded by two plates in four of 

 the areas and three plates in the azygous ; above which tlie plates are 

 much smaller. As stated above, the radials are connected with the in- 

 terradials, as high as the top of the tertiary i-adials, which is the 

 base of the arms ; at this point four or five of the last inter 

 radial plates connecting with each tertiary radial form part of a 

 flexible fold, which is continued onward four or five plates further 

 into a cornu, the point of which approximates to that having its rise 

 on the opposite side of the same interradius ; these folds and cornu a 

 were, at first sight, supposed by me to be arras. 



When ]Mr. Wachsmuth defined this genus the arms and the vault 

 were unknown. The specimens figured show these features in a very 

 satisfactory manner. The vault is seen to be composed of very small 

 plates, and with an anal opening near the ambulacral centre. There is 

 no proboscis and the vault and arms approximate to those of Glypto- 

 crinus. 



The cup-plates are smooth and gibbous. The radial plates have 

 obtuse ridges, following the longitudinal axes of the rays, much ele- 

 vated at the sutures but almost obsolete in the middle of the plates. 

 Trenton Formation. — All the specimens collected by the author 

 ■on Division street, Rochestei ville. 



