F. A. Bather — Ordovician Crinoids. 73 



Dicj'clica with certainty, though the regularity of the cup is in 

 favour of the latter. A similar disposition of the anal tube is found, 

 among Monocyclica, only in Iocrinus ; among Dicyclica, only in 

 Merocrinus. So far as geological horizon is concerned, the specimen 

 might belong to either of these genera. Iocrinus is at present known 

 from the Hudson River Group of Ohio and from the Trenton 

 Limestone of New York. Merocrinus has been found only in the 

 Utica Shale of Ohio and in the Trenton Limestone of New York. 

 Neither genus has hitherto been recorded from Europe. 



Iocrinus Me-roc-rzrzus 



Comparing specimen A with Iocrinus and Merocrinus, we note 

 that the anal tube of Iocrinus is composed of numerous hexagonal 

 plates, set along the sides of the mid-rib, as one may call it, that 

 starts from the arm. Specimen A, however, shows no traces of 

 these lateral plates, although it is so preserved as to have done 

 so had such been present ; on the contrary, the anal tube appears 

 to have been a simple narrow tube, precisely as in the known 

 species of Merocrinus. All known species of Iocrinus further 

 resemble one another in the marked imbrication of the brachials ; 

 while the species of Merocrinus have as a rule smooth brachials, 

 although M. curtus, as figured and described by Uliich (" Dendrocrinns 

 curtus," Jonrn. Cincinnati Soc. Nat. Hist., II, p. 18, pi. vii, 

 fig. 14, 1879), has brachials " prominent at the superior lateral 

 angle." The very slight development of this feature in the Mincop 

 specimen is therefoi - e characteristic of Merocrinus rather than of 

 Iocrinus. In other respects the specimen might belong to either 

 genus ; but the balance of evidence favours its reference to 

 Merocrinus. 



In minor characters specimen A differs from the known species 

 of both Iocrinus and Merocrinus. From Iocrinus crassus and 

 I. subcrassus it is distinguished by its less robust appearance, less 

 wide radials, and less imbrication of the arms, as well as by the 

 above-mentioned character of the anal tube. In a less degree 

 the same characters separate it from I. trentonensis, a species 

 which, according to Walcott's figure (Regent's Report, N.Y. State 

 Mus., XXXV, p. 210, pi. xvii, figs. 7 and 8, 1884), further differs 

 in the possession of a slight ridge along the back of the radials 

 and primibrachs. 



From Merocrinus curtus specimen A is clearly distinguished by 

 the regular dichotomy of its arms, for in M. curtus there are simple 

 armlets, "about half as stout as the main arm from which they 

 spring." The cup is also lower in M. curtus. It was doubtless 

 a mere slip that made Mr. Ulrich describe the anals of this species 

 as rising from the right side of the right posterior arm, instead 



