BRACHIOPODA. 87 



but not a denned ridge. The number of spines on the individual figured has been sixty 

 or more." 



Remarks — The specimens identified as P. spinulicosta Hall are rare and in most 

 cases not well preserved. They are all small. 



Occurrence — Mineola of Montgomery and Warren Counties. 



Superfamily Pentameracea 



Family Pentameridae 



Genus Pentamerella Hall 



Pentamerella arata (Conrad) 



Plate 16, figure 16; plate 17, figures 17-23 



1841. Atrypa arata Conrad, Fifth Ann. Rep. Geol. Survey N. Y., p. 55. 



1867. Pentamerella arata Hall, Pal. New York, IV, pt. 1, p. 375, pi. 58, figs. 1-21. 



1897. Pentamerella arata Schuchert, U. S. G. S. Bull. 87, p. 302. 



1901. Pentamerella arata Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. Rept., p. 



615, pi. 7, fig. 2. 

 1909. Pentamerella arata Grabau and Shimer, North American Index Fossils, I, pi. 



277, fig. 337. 



Hall's description — "Shell ovate, more or less convex or gibbous, becoming arcuate 

 ovoid in old shells ; the width greater or less than the length ; hingeline variable. Ventral 

 valve gibbous and somewhat regularly convex in the young shells, becoming ventricose 

 in old shells, with a mesial sinus which is more or less developed. In old shells the form 

 is extremely arcuate and the beak strongly incurved ; in shells of medium size the beak is 

 obtuse, limiting the apex of the triangular fissure. There is a narrow area bordering the 

 fissure and the space on either side between the hingeline and its apex is often flat- 

 tened and sometimes distinctly limited by a faint elevation ; fissure large and nearly 

 covered by the beak of the opposite valve. Dorsal valve in young shells more or less 

 convex, and sometimes gibbous in the upper part, and often moderately convex in older 

 shells; mesial fold usually well defined in the lower half of the valve, sometimes reaching 

 nearly to the apex; in young shells there is rarely a short sinus in place of the mesial 

 elevation. Surface plicated by rounded or angular plications, which sometimes reach 

 nearly or quite to the beak but are often only developed below the first third of the 

 length; plications usually bifurcated; the bifurcations irregular or unequal. The interior 

 of the ventral valve has an elongate spoon-shaped pit, the inner extremity of which is 

 free for a considerable extent and the upper part supported on the central septum 

 which usually extends less than half the length of the shell from the apex. In the dorsal 

 valve the crura or lamellae are joined at their bases, making a V-shaped trough or pit, 

 which is attached to the valve in its upper part and continues sessile for about one-half 

 the length of the shell." 



Remarks — This species is abundant in the Mineola. It is extremely variable in 

 size, shape and plications. The largest specimen is 28 mm. long by 35 mm. wide, while 

 average specimens are about 14 mm. long by 14 mm. wide. Some specimens have no 

 more than 8 plications to a valve while others have 25; in some the plications are very 

 strong (see figure 18) while in others they are scarcely visible (see figure 22). In some 

 the plications extend two-thirds the length of the shell while in others they are confined 

 to the margin. 



Occurrence — Abundant in the Mineola of Montgomery and Ralls Counties. 



