8 PALvEONTOLOGV OF NEW-YORK. 



BRACHIOPODA OF THE MEDINA SANDSTOxNE. i 



This rock contains comparatively few species of fossil shells. At the time the Report of the 

 Fourth District was published, scarcely more than half a dozen species were known in the rock. 

 The most diligent search has little more than doubled that number to the present time ; and it 

 is scarcely possible that many more will ever be discovered, unless some peculiarly favorable 

 locality should be found. The almost entire absence of calcareous matter, and more particularly 

 the abundance of ferruginous coloring matter, has been unfavorable to the development of 

 testaceous organic forms. 



388. 12. LINGULA CUNEATA. 



Pl. IV. Fig. 2 a, b, c, e. 



Lingula cuneata. Conrad, Annual Report of 1838, p. 113 (name without description); of 1839, 



p. 64. 



Shell cuneiform, very acute at the beaks ; margins nearly rectilinear, and converging uni- 

 formly from near the base to the beak ; base lightly curved ; the valves convex on the upper 

 half, but flattened or compressed towards the base ; surface longitudinally striated. 



This species of Lingula is readily distinguished from any of the other species, bj- its acutely 

 cuneate form. It occurs in great numbers in some gray layers about fifty feet below the upper 

 surface of the rock ; but the shell is usually more or less exfoliated, and the striae partially or 

 wholly destroyed. The shell is translucent and usually of a light color, particularly in the light 

 gray sandstone. It is so abundant that some layers at Medina are almost entirely composed of 

 it, the laminee of sand separating each layer of shells being scarcely a quarter of an inch thick. 



In another situation near Lockport, this species occurs scattered over large surfaces of the 

 sandstone layers, still remaining in the position they were deposited by the advancing and re- 

 tiring waves upon the beach. In this position they are scattered over wide surfaces, and on 

 successive layers often scarce half an inch in thickness. The surfaces of these layers are marked 

 by wave lines, indicating the limit of the advancing waves. 



Fig. 2 a. A specimen of large size, nearly destitute of a shell. 



Fig. 2 i. A small fragment of sandstone, showing upon its surface three individuals of different 

 size. 



Fig. 2 c. A small individual, preserving the shell nearl)' entire. The two last are associated with 

 a small species of Cytherina, fig. 8. 



Fig. 2 e. A small fragment from a slab of sandstone, where the Lingulje have been drifted by 

 the waves. From the beak of each one extends a small ridge of stone which ac- 

 cumulated here, protected by the shell during the receding of the wave*. 



* For a fall description of the phenomena connected with these shells, wave-lines, etc., see Report on the Geolog)' 

 of the Fourth District, 1843, p. 52 et seq. 



