RETICULARIA 429 



from the beak to about the middle of the valve, being about twice the 

 length of the dental lamellae; the muscular scars are obscure, being 

 scarcely differentiated from the general inner surface of the valve ; the 

 shell itself is thin so that the concentric markings of the external surface 

 are clearly shown upon the internal casts, which are also marked by fine, 

 irregular, more or less inconspicuous radiating costse. 



Brachial valve less strongly convex than the pedicle, the greatest con- 

 vexity posterior to the middle, the surface curving somewhat abruptly to 

 the cardinal margin and rather gently to the lateral and anterior mar- 

 gins, moderately compressed towards the cardinal extremities; mesial 

 fold obscure or obsolete, when present it is very low, rounded on top, and 

 is ill-defined laterally; the beak is small, short, and a little incurved, the 

 umbonal region projects a little beyond the cardinal margin; cardinal 

 area narrow, nearly horizontal in position. Internally the cardinal pro- 

 cess is scarcely differentiated; a median septum which rapidly becomes 

 only a slight, raised rib along the floor of the valve, extends to a point 

 between one-third and one-half the length of the valve from the beak; 

 at the beak the cardinal process is flanked by a pair of rather strong but 

 short crural plates which join the median septum ; the muscular scars are 

 scarcely or not at all differentiated from the general inner surface of the 

 valve. 



The surface of both valves is marked by moderately broad, concentric 

 bands which are beset with closely arranged fimbria? or fine spines, those 

 of successive bands being imbricating in arrangement. 



Remarks. This species is a close ally of R. pseudolineata, but is always 

 smaller and is commonly proportionally thicker and narrower. Inter- 

 nally the radiating costse of the shell which are so characteristic in 

 R. pseudolineata are much less strongly developed than in that species. 

 In the condition of preservation in which it is commonly found, the sur- 

 face of the shell is exfoliated and the exact nature of the concentric rows 

 of spines is not clearly shown, but they are probably of the double-tubed 

 type similar to those of R. pseudolineata. 



The species differs from R. tenuispinata of the Ohio Waverly, in its 

 greater proportional length and in the less conspicuous development of the 

 internal radiating costse, that species being more nearly like a diminutive 

 R. pseudolineata. 



Horizon. Kinderhook. 



RETICULARIA PSEUDOLINEATA (Hall) 

 Plate LXXIV, Figs. 1-11 ; Plate LXXV, Fig. 20 



1858. Spirifer pseudolineatus Hall, Geol. Iowa, vol. 1, pt. 2, p. 645, pi. 20, 



fig. 4. 

 1883. Spirifera pseudolimeata Hall, Rep. N. Y. State Geol. for 1882, pi. 



(36) 61, figs. 28-30. 



