Description of Fom^ JVeiv Species of Silurian Fossils. 141 



of the interbracliials has a length about one half greater than the 

 diameter of the dome. It expands rapidly as it approaches the top of 

 the interbrachials, and here we have the evidence in the projections 

 and the furrows, that the interbrachials w^ere firmly interlocked with 

 the plates or pieces that surrounded this canal. 



The canal extends above the top ot the interbrachials forming a 

 dome, slightly drawn to one side, and having a height about equal to 

 its basal diameter. This dome was surrounded, as it appears from our 

 specimens, by five large plates. 



It has been considered, by Prof. Hall, that the genus Hypanthocrinus 

 of Phillips, is a synonym for Eucalyptocrinus^ founded thirteen 3^ears 

 earlier by Goldfuss. Angelin and other European authors, however, re- 

 tain both generic names, referring to the former such species as have 

 an expansion of the canal at the top of the interbrachials, and a dome 

 covering this expansion. Our species possesses all the characters of 

 Hypanthocrinus^ and I have retained the name, in a subgeneric sense, 

 because there are a number of species constructed upon this plan, which 

 may thus be collectively distii;kg'uished from the t3^pical Eucalypto- 

 crinus. 



This species was collected in the magnesian limestone of the Nia- 

 gara Group, at Chicago, 111., hy W. C. Egan, Esq., of that city, in 

 whose honor I have proposed the specific name. He ver3^ kindl^^ pre- 

 sented some specimens to the Cincinnati Society of Natural Histor^^ 

 and to the author. 



Myelodactylus bkidgeportensis, n. sp. 



(Plate IV., fig. 2, a dextral specimen showing the finger-like processes extending over 

 the inner whorls; fig. 2a, a sinistral specimen showing the radiate structure; fig. 25, a dex- 

 tral specimen having the finger-like processes removed so as to show the larger and smaller 

 whorls, and their union at the central part of the disk; figs. 2c and 2c?, showing the radi- 

 ate structure; fig. 2e, magnified view of a fractured specimen.) 



This species is possessed of a coiled and radiate structure of an ap- 

 parently complicated character. The coil is discoidal and both dex- 

 tral and sinistral, in different specimens. There are nearly four whorls, 

 in the best specimens examined. 



The coil consists of a double series of plates which unite at the central 

 part of the disk. From every two plates of the outer series, there arises a 

 finger-like process, which extends over the next inner whorls, toward the 

 center of the disk. Beneath these overlapping finger-like processes 

 there is a passage, inclosed by reason of the whorls being brought in- 

 to contact b}" the inner series of plates. The inner series of plates are 

 about one third the size of the outer series, and connect the latter 



