210 N. Y. State Museum of Natural History. 



Merocrinus corroboratus, n. sp. 



Plate 17, fig. 6. 



Body slender, elongate. Calyx small, broad at the base, increas- 

 ing slightly in width above. 



Underbasals pentagonal, of medium size, and having a transverse 

 diameter twice as great as the height. Basals larger, broadly hexa- 

 gonal, alternating with the underbasals, and supporting above the ' 

 pen tagonah radial plates which have their width and hight subequal 

 and their lateral margins scarcely uniting in the type specimen. The 

 first plate, above the radial, of the right postero-lateral ray, is penta- 

 gonal and supports the brachial plates and the posterior plates of the 

 anal tube as in Merocrinus typus. The anal plates being much 

 more slender, but not showing any evidence of the attached portions 

 of an anal tube, such as exists in the genus Iocrinus. 



The arms are slender and bifurcate as in Merocrinus typus. 



The column near the calyx is formed of thin round plates, the 

 plates gradually increase in thickness below until it nearly equals 

 one-half of their transverse diameter. 



The anterior side of both this and the preceding species is un- 

 known. 



Formation and locality. Trenton limestone, Trenton Falls, New 

 York. 



Genus IOCRINUS, Hall.* 



Two species of this genus have been described. I. crassus and 

 I. subcrassus from the Hudson River Group of Illinois and Ohio. 

 /. subcrassus is distinguished from I. crassus by its smaller size, 

 different aspect of the arms and less robust appearance while the 

 Trenton limestone form of New York has more slender arms, a less 

 robust appearance than /. subcrassus, and it also occurs at a lower 

 geological horizon, and at a distant locality. In many respects, 

 however, the three forms are but varieties of one species. At present 

 it is convenient to designate them by separate names. 



Iocrinus Trentonensis, n. sp. 

 Plate 17, figs. 7, 8. 



This species agrees so closely in all essential characters with Iocri- 

 nus crassus and I. subcrassus, that a detailed description is unnec- 

 essary. 



The small pentagonal basals alternate with the large pentagonal 

 radials which have their upper margins broadly truncated. Brachials 

 four or five in each ray, the upper plate supporting the first division 



* As defined by Wachsmutk and Springer. 



