CRUSTACEA. 217 



and without the median ridge. These different forms of plates have been 

 found in close proximity leaving little doubt of their coherence in the same 

 individual, probably being from separate vertical ranges in the composition of 

 the capitulum. The elongate form finds a close parallel in some of the Bohe- 

 mian species, as Plumulites Bohemicus, Pl.frate.rnas, PL compar, Barrande, although 

 the latter attained a considerably greater size, and it appears probable that the 

 broader plate here described is homologous with the plates termed by M. Bar- 

 rande the valve frnesln'e, found in association with the plumate plates in well- 

 preserved specimens from the etage D. This plate was however regarded by 

 Barrande not as a member of a range of similar plates but as isolated among 

 the other plates composing the capitulum. 



The scales of Turrilepas Devonicus are small, the elongate form measuring 3.5 

 mm. in length and 2.5 mm. across the base, the broader form 2.5 mm. in length 

 and 2 mm. in width. 



Distribution. Hamilton group. In the shales and limestones near the base of 

 the Hamilton shales : Canandaigua and Centerfield, Ontario county. 



Turrilepas squama, n. sp. 



PLATE XXXVI, FIGS. 5-8. 



A few scattered plates exceeding in size any belonging to the associated 

 species appear to represent a distinct form. These are broadly sub-triangular, 

 having a width nearly equal to the length. The best preserved examples are 

 valves fenestrees, having the nucleus sub-apical. The earliest of the concen- 

 tric striae are nearly circular, becoming sinuous, more transverse and more 

 closely crowded near the basal margin. Along the posterior margin the striae 

 present the appearance of being " gathered," but they become obsolete before 

 reaching the anterior margin. 



The surface is nearly flat, with indications of a low sinus near the middle of 

 the valve and toward the posterior edge. The other plates referred to this 

 species have the same general form, and the nucleus apical, one of them being 

 abruptly deflected toward the anterior margin. They all agree in the character 



