Description of Four New Species of Silurian Fossils. 143 



sometimes three minute grooves or perforations communicating with 

 the muscular impression upon the upper surface." 



Angelin referred three species to the genus Myelodactylus, viz., M. 

 gracilis^ 31. heterocrinus and J/, interradialis*. He described the 

 generic characters as. follows : "Corpus tenerum, elongatum. Cal3^x 

 C3^athoideus. Basalia tria. Parabasalia qui n que, polygona. Radialia 

 primaria quinque, unicam zonam formantia ; secundaria per duas 

 series ; superiora triangula, brachiifera. luterradialia duo. Brachia 

 longissima, subfiliformia, repetito-dichotoma, articulis simplicibus. 

 Tubus ventralis distinctus, articulatus. Columna crassa, convoluta, 

 articulis tenuissimis, cirrhis numerosis, moniliformibus." 



His species are all small and slender, and very much resemble some 

 species of Heterocrinus. They certainl}^ have no generic relation with 

 llyelodactylus. 



Pal^aster miamiensis, n. sp. 



(Plate IV., fig. 3.) 



Pentagonal ; ra3^s about one and a half times the diameter of the 

 body, or about 9-lOths of an inch; diameter of the bod}^ about 6-lOths 

 of an inch; breadth of a ray at the point of junction with the body a 

 little more than half the diameter of the body, or about 7-20ths of an 

 inch; rays obtusely pointed. 



Marginal plates wider than long, and numbering about twelve in the 

 length of half an inch from the body. Two marginal plates form the 

 junction of the ra^^s. Ambulacral farrow wide, the plates being more 

 than twice as long as wide. There are about 18 ambulacral plates 

 in a length of one half inch, and each one is provided with an angular 

 ridge tapering from the marginal plates to the furrow. 



This species is founded upon a single specimen, showing only the 

 ventral part of the bod^', and hence the other parts are unknown. 

 It bears some resemblance to P. granulosus , but on comparison with 

 good specimens in my own collection I found it essentially distinct. 

 In the marginal plates it bears some resemblance to P. longihracliiatus, 

 though even in this respect the two species are distinct. 



The specimen was found near Wa3aiesville, on the Miami river, in 

 the upper part of the Hudson River Group, and belongs to the collec- 

 tion of I. H. Harris, Esq., of that place. 



Bythopora nashvjllensis, n. sp. 



(Plate IV. s fig. 4, natural size; fig, 4a, magnified view.) 

 In this species the branches are cylindrical, of nearl3^ equal size, and 



* Iconographia Crinoideorum in stratis Suecise Siluricis fossilium. 



