208 



margin ; second radials hexagonal, not half as large as 

 the first, wider than high ; third radials smaller than the 

 second, pentagonal, wider than high, supporting arm- 

 plates on the upper sloping sides. First iuterradials larger 

 than the second radials, hexagonal, supporting two plates 

 in the second range. 



Surface finely and beautifully striated by fine sharp, un- 

 dulating strias, about twelve of which traverse the lower 

 side of the first radial plate, meeting similar ones from the 

 basal plates ; the apices or junction of the strise are in the 

 line from the centre to the angles of the plates in the 

 basal, first radial and interradial plates, while on the surface 

 of the smaller plates these lines are sometimes broken into 

 granules. 



This species resembles the M. ornatus from the shales of 

 the Niagara group at Lockport, N. Y.; but the rays are more 

 spreading and the surface markings are finer. 



BRACHIOPODA. 

 GENUS CRANIA (Lamarck). 

 Crania siluriana (Hall). 



Shell subcircular or transverse, very depressed, conical ; 

 apex excentric, slightly curved, situated one third the 

 diameter of the shell from the cardinal border. Exterior 

 surface of upper valve smooth, with concentric lines of 

 growth. Ventral or lower valve consisting of little more 

 than a thickened rim, deeply marked on the cardinal mar- 

 gin by the somewhat large and distant posterior adductor 

 muscular scars ; the substance within the thickened bor- 

 der is not sufficient to preserve the muscular or vascular 

 markings. 



Transverse diameter of full grown specimens nearly 

 three fourths of an inch ; elevation of upper valve of the 

 same a little less than one fourth of an inch. Where well 

 preserved the surface is minutely granulose or subpunctate. 



