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.fraternus, 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 fenestree, found in association with the plumate j)lates 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 fenestrSes, 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 
