BRACHIOPODA. 407 



KafliH-squina alternata, var. loxorhytls.] 



in great measure, to the larger size attained and the greater thickness of the shell. 

 Still, these differences are so conspicuous that it may prove desirable to distinguish 

 the Hudson River forms by a varietal name. According to Hall,* the large thick- 

 shelled variety occurring at Cincinnati is known to collectors there as Leptcena pon- 

 derosa. This name is very appropriate and if a separation is to be made it should 

 be used, unless the objection is made that it was not defined; still, if the species is 

 ascribed to Hall, there could be no doubt as to what form is meant. In England and 

 Ireland this shell is commonly repreesented in the Caradoc and Lower Llandovery 

 by Orthis expansa Sowerby, which is abundantly illustrated by Davidson in his 

 monographs.! 



In the Trenton shales R. alternata, when the exterior alone is shown, is not 

 always easily distinguishable from large and not very convex individuals of R. minne- 

 sotensis. Usually, however, the stronger convexity and smaller size of the latter form 

 and the five internal ridges of the dorsal valve will serve to separate them. 



Formation and locality. A few specimens have been found in the Trenton limestone at St. Charles 

 and it also probatly occurs elsewhere in these beds in Minnesota. From the Trenton shales at Minneapolis, 

 St. Paul, Cannon Falls, Lanesboro and Preston, Minnesota; not rare at the base of the Galena in the 

 shales at several localities south of Cannon Falls, and at Kenyon and Fountain. Near the top of the "Lower 

 Blue beds" at Mineral Point, and probably elsewhere in Wisconsin. It also occurs in the Trenton at 

 Dunleith, Illinois; Kentucky; Tennessee; New York, and Canada. Very common in the Hudson River 

 group in Ohio, Indiana, Kentucky, Tennessee, New York and Anticosti. 



Collectors. C. L. Herrick, H. V. Winchell, W. H. Scofleld and the writers. 

 Mu. Reg. Nos. 181, 287, 3396, 4037, 5859, 6761, 8151-8154. 



RAFINESQUINA ALTERNATA, var. LOXOEHYTIS Meek. 



PLATE XXXI. FIGS. 35-37. 



1873. Strophomena alternata, var. loxorhytis MEEK. Palseontology of Ohio, vol. i, p. 91. 

 1875. Strophomena alternata, var. loxorhytis MILLER. Cincinnati Quarterly Journal of Science, 



vol. ii, p. 53. 



Original description: "Attains a larger size [than R. alternata], moderately con- 

 vex antero-centrally, or rather depressed; much extended on the hinge-line, with 

 lateral extremities acutely angular, flattened and scarcely deflected; area very nar- 

 row; both valves marked near the cardinal margin, toward the lateral extremities, 

 by six to eight distinct, very oblique wrinkles on each side." 



The shells referred to this variety agree in all essential features, except that the 

 convexity is somewhat greater than in the Ohio specimens. R. kingi Whitfield^: is a 

 closely related species, also occurring in the upper portion of tlie Cincinnati group> 

 but it can be distingushed at once from R. alternata, var. loxorhytis by its fine and 

 equal strise. 



*Pal. N. Y.. vol. i, p. 104, pi. xxxi, figs, la, 11, 1m, 1847. 



t British Silurian Brachiopoda, p. 312, pi. XLV. figs. 110. 



t Stroplwmena kiimi, Geol. Wise., vol. iv, p. 261, pi. xu, flgs. 15, 10. 



