CLIOTHYRIDINA 479 



crowded than in typical examples of C. hirsuta. The shell is also less 

 apt to exhibit the slightly pentagonal outline which is commonly assumed 

 by C. hirsuta. 



Horizon. Kinderhook oolite and lower Burlington white chert. 



CLIOTHYRIDINA HIRSUTA (Hall) 

 Plate LXXX, Figs. 13-24. 



1857. Spirigera hirsuta Hall, Trans. Albany Inst., vol. 4, p. 8. 



1882. Atkyris hirsuta Whitfield, Bull. Am. Mus. Nat. Hist., vol. 1, p. 49, 



pi. 6, figs. 18-21. 



1883. Athyris hirsuta Hall, 12th Ann. Rep. Geol. Surv. Ind., p. 328, pi. 



29, figs. 18-21. 



1884. Athyris hirsuta Walcott, Pal. Eureka Dist, p. 222, pi. 18, fig. 5. 



1894. Cliothyris Roysii Hall and Clarke, Int. to Study of Brach., pt. 2, 



pi. 35, fig. 9 (not fig. 10). 



1895. Cliothyris Eoysii Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 46, 



fig. 23 (not fig. 24). 

 1895. Cliothyris hirsuta Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 46, 



figs. 25-28. 

 1906. Cleiothyris hirsuta Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 1320, 



pi. 19, figs. l-la ; pi. 22, figs. 18-21. 



Description. Shell small, lenticular, suborbicular, subquadrangular or 

 subpentagonal in outline, length and breadth usually subequal, the great- 

 est width at about the mid-length of the shell; hinge-line much shorter 

 than the greatest width of the shell, cardinal extremities rounded, the 

 two valves subequally convex. The dimensions of a specimen of average 

 size are : length 9 mm., width 9.2 mm., thickness 6 mm. 



Pedicle valve most convex posterior to the middle, the surface curv- 

 ing abruptly from the umbonal region to the cardinal margin and more 

 gently to the lateral and anterior margins ; the beak small, slightly in- 

 curved, pierced by a subcircular foramen which lies in a plane oblique to 

 the plane of the valves; delthyrium broad, filled by the beak of the 

 opposite valve, connected with the foramen at its apex; mesial sinus 

 obsolete, but in some of the larger examples the mesial portion of the 

 shell is slightly flattened. 



Brachial valve ne'arly equally convex with the pedicle, the greatest 

 convexity posterior to the middle, the surface curving abruptly from 

 the point of greatest convexity to the cardinal margin, and more gently 

 to the lateral and anterior margins; mesial fold obsolete or represented 

 only by a narrow, median, flattened region which is more or less ill- 

 defined laterally; beak strongly incurved beneath that of the opposite 

 valve, and nearly or quite filling the delthyrium of that valve. 



The surface markings of both valves consist of thin, crowded, con- 

 centric, closely imbricating, lamellose extensions of the shell, which 



