14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



R. 25 E., Bisbee Quadrangle, Cochise County, Arizona; Rancho 

 Nuevo, 3 miles east of Santa Rosalia, Sonora, Mexico. 



Discussion. — This species is characterized by its compact form, 

 small foramen, moderately strongly uniplicate commissure, flatly con- 

 vex brachial valve and deep pedicle valve. No other species of this 

 genus is now known in North America to which this one can be com- 

 pared. The species most like P. occidentalis outside of North America 

 is "Waldheiniia" tamarindus (Sowerby) from the British Isles. A 

 variety of forms now appears under this name in the British Isles, 

 but specimens of P. tamarinda from Faringdon, England, are most 

 like the American species. They differ, however, in having a narrower 

 anterior region, a larger foramen and much less convex pedicle valve. 

 The development of the median septum in the interior of both the 

 British and American forms is very slight. 



PSILOTHYRIS TAMARINDA (Sowerby) 



Plate 3C, figure 25 



The interior of a brachial valve is introduced for comparison with 

 P. occidentalis. Note the low and reduced median septum and the 

 short undivided hinge plate. 



Horizon and locality. — Cretaceous (Aptian — Lower Green Sand), 

 Faringdon, Berkshire, England, 



REFERENCES CONSULTED 

 Bosquet, J. 



1859. Monographic des brachiopodes fossiles du Terrain Cretace superieur 

 du Duche de Limbourg. Haarlem. 

 Cobban, W. A., and Reeside, J. B., Jr. 



1952. Correlation of the Cretaceous formations of the western interior of 

 the United States. Bull. Geol. Soc. America, vol. 63, No. 10, pp. 

 1 01 1 -1044. 

 Davidson, T. 



1852-1855. A monograph of the British fossil Brachiopoda. Part 2. The 



Cretaceous brachiopods. Palaeontographical Soc. 

 1874. A monograph of the British fossil Brachiopoda. Vol. 4, Part i, Sup- 

 plement to the Recent, Tertiary and Cretaceous species, pp. 17-72. 

 Deslongchamps, E. E. 



18S4. Etudes critiques sur des brachiopodes nouveaux ou peu connus. Art. 8. 

 Note sur les modifications a apporter a la classification des 

 Terebratulidae. 

 Elliott, G. F. 



1947. The development of a British aptian brachiopod. Proc. Geol. Assoc, 

 vol. 58, pt. 2, pp. 144-159- 

 MuiR-Wooi). H. M. 



1934. On the internal structure of some Mesozoic Brachiopoda. Philos. 

 Trans. Roy. Soc. London, ser. B, vol. 223, pp. 511-567. 



