MARIOCRINUS. 219 



III. Family MELOCRINID^E, Zittel, 1880. 

 1. Genus MARIOCKINUS, Hall, 1859. 



To what genus the following species belongs seems very doubtful. Being 

 monocyclic with four basals and presumably without an anal in the radial ring, 

 it is however, excluded from Melocrinus by its uniserial arms, and their mode of 

 branching. 



The Silurian genus Mariocrinus l perhaps presents the least difficulty. Accord- 

 ing to Wachsmuth and Springer it differs from Melocrinus in having uniserial 

 arm-plates. Some of its arms, however, are stated to be simple, whereas those 

 of our fossils probably all fork once a long way up. The number of plates, 

 moreover, which are contained in the cup in our species seems very much fewer. 



1. MARIOCRINUS? MUNDUS, n. sp. Plate XXXIV, fig. 5? and Plate XXXVII, 



figs. 6, 7. 



Description. Stem round, very long, consisting of rather long, uniform, rather 

 convex columnars in the lower parts, which become very short and more convex 

 near the cup, the uppermost joint being apparently formed only halfway round. 

 Margins of columnars very strongly crenulated. Dorsal cup elongate, vasiform. 

 Basals four, about as long as their width. Radials five, very large, hexagonal or 

 heptagonal, longer than wide, with flat upper margins. First primibrachs much 

 smaller than the radials, pentagonal, axillary. Secundibrachs slightly smaller 

 than the primibrachs, pentagonal, included within the cup, bearing two arms. 

 Interambulacral plates (in one observed area), one resting on the shoulders of two 

 radials, and about the same size as and at rather a lower level than the first 

 primibrachs, hexagonal, bearing on its shoulders two much smaller inter- 

 ambulacrals of the second row. Anal side unobserved. Arms twenty ? uniserial, 

 apparently short (about one and a half times the length of calix), tapering, 

 composed of alternating wedge-shaped plates, bifurcating at about the fifteenth 

 joint, and without any visible signs of pinnules. 



Size. A specimen with stem and arms measures about 110 mm., the cup being 

 about 7 mm., and the arms 14 mm. 



Localities. A single specimen from Croyde Rocks is in my Collection ; and in 

 the Barnstaple Athenaeum is a doubtful specimen from Braimton (PI. XXXIV, 

 fig. 5) showing a few plates of the cup and parts of the stem and arms, which 

 possibly may belong to the same species. 



1 1881, Wachsmuth and Springer, ' Proc. Acad. Nat. Sci. Philad.,' 1881, p. 288. 



FF 



