BRACHIOPODA. 109 



1894. Cyrtina triquetra Hall and Clarke, Pal. New York, VIII, pt. 2, pi. 28, figs. 34, 35. 

 1897. Cyrtina triquetra Schuchert, Bull. U. S. Geol. Surv., 87, p. 199. 

 1909. Cyrtina triquetra Greger, Am. Jour. Sci., XXVII, p. 376. 



Hall's description — "Shell small, pyramidal; cardinal extremities somewhat salient. 

 Ventral valve extremely elevated, the beak slightly incurved; sinus deep, angular or 

 subangular, bounded on either side by strong plications; area large, forming a nearly 

 equilateral triangle, the base being scarcely longer than the sloping sides; foramen 

 narrow, slightly open at base, and closed for half its length by a pseudo-deltidium. 

 Dorsal valve depressed convex, semi-circular or semi-oval, with a strongly elevated 

 mesial fold which is bounded by a deeper groove than those separating the plications. 



Surface marked by seven or eight plications on either side of the mesial fold, and 

 by nine on either side of the mesial sinus, and these are crossed by fine imbricating 

 lamellose striae; the entire surface granulose or punctate." 



Remarks — Specimens identified as Cyrtina triquetra are rare in the Snyder Creek 

 shale. The area is somewhat higher than in the type of C. triquetra, the number of 

 plications is 6 to 8, and occasion lb 9 on either side of the fold and sinus, the outer ones 

 usually poorly defined. On the type of C. triquetra the outer plications on the brachial 

 valve are poorly defined. In most of the Snyder Creek specimens the pseudo-deltidium 

 extends about half the height of the delthyrium, but in the one shown in figure 12, it 

 nearly closes it. 



Family Athyridae 



Genus Athyris McCoy 



Athyris fultonensis (Swallow) 



Plate 17, figures 1-4. 



1860. Spirigera Fultonensis Swallow, Trans. St. Louis Acad. Sci., I, p. 650. 

 1860. Spirigera minima Swallow, Ibid. p. 649. 



1894. Athyris vittata Keyes, Geol. Survey Missouri, V, pt. 2, p. 90, pi. 41, fig. 1. 

 1897. Athyris fultonensis Schuchert, Bull. U. S. Geol. Surv., 87, p. 147. 

 1909. Athyris fultonensis and Athyris minima Greger, Am. Jour. Sci., XXVII, pp. 

 376-377. 



Swallow's description — "Shell small, lenticular, flattened towards the anterior 

 and lateral margins, forming there a thin sharp edge at the junction of the valves. 

 Ventral valve suborbicular, moderately convex, highest near the beak; mesial sinus 

 obsolete or entirely wanting; beak short, incurved; perforation small, orbicular. Dorsal 

 valve smaller, orbicular, most convex near the beak; beak small, incurved, breaking the 

 periphery of the perforation of the opposite beak. Surface regularly marked with 

 numerous, concentric, lamellose, granular plications and fine concentric striae; the 

 striae are observed on well preserved specimens only. 



Length, .50; breadth, .53; thickness, .28. 



This fossil is most like Sp. hirsuta of Prof. Hall; but it may be distinguished by its 

 greater thickness near the beaks, and by the sharp thin edge found at the junction of 

 the valves. 



Abundant in some beds of the Hamilton rocks of Callaway County." 



Remarks — Most paleontologists use Athyris vittata Hall as a synonym for A. 

 fultonensis (Swallow) and the writer followed that precedent until he had collected 

 hundreds of specimens of both species. Swallow described two species of Athyris from 

 Callaway County, Missouri. A. fultonensis and A. minima. Both are listed from the 

 Hamilton rocks of Callaway County. As the types were burned it is impossible to 

 compare with them, but there can be no question about the species. The writer has 

 examined more than 500 good specimens of Athyris from Callaway County. Tfie small 

 specimens grade into the large with no perceptible differences save in size, and A. 

 minima becomes a synonym of A. ftdtonensis. 



