Brachiopoda of the Cincinnati Group, 53 



convexity. Variety frada, of Meek, I regard as a good species, and 

 var. nasuta (Conrad), var. alternistnata (Hall), and var. loxorhytis 

 (Meek), I regard as good varieties, possessing somewhat constant char- 

 acters, to separate them from the type species. 



Strophomena alternata var. 7ictsuta — (Conrad, 1842). 



Shell subtrigonal in outline, more deeply concave on the dorsal 

 side, and more extremely convex on the ventral side than typical 

 forms of alternata; an obtuse, undefined, mesial ridge on the ventral 

 valve continues to the middle of the front, giving the shell its sub- 

 trigonal outline. The shell is usually thick and heavy, and strongly 

 marked in the interior with muscular scars and furrows. 



Length of an average specimen, 1.30 inches; breadth, 1.50 inches; 

 convexity, 0.54 inch. 



Its range commences about 400 feet above low water-mark, and 

 terminates within about 200 feet, as near as I have been able to 

 ascertain. 



Strophoinena, alternata var. alternistriata — (Hall, 1847). 



Shell semi-oval, wider than long, cardinal line extended, lighter, 

 thinner, and less abruptly curved and thickened on the margin than the 

 typical alternata ; striae more uniform in size and finer than in alternata 

 proper ; and the shell has a shining luster, like L. sericea. 



Its range seems to be about as great as that of the alternata, and I 



't3^ 



am not sure but that the form found within 200 feet of low water- 

 mark should rather be classed with this variety than with the typical 

 alternata (though its striae are coarse and hinge line truncated), in which 

 latter case its range would even be the greatest, though it is much 

 less abundant. 



Strophomena alternata var. loxorhytis — (]Meek, 1873). 



Shell large, moderately concave on the dorsal, and convex on the 

 ventral valve antero-centrally ; hinge line extended with lateral 

 extremities acutely angular and flattened ; both valves marked near 

 the cardinal margin, toward the lateral extremities, with six or eight 

 distinct, more or less oblique wrinkles, similar to those on Hemipronites 

 subtenta. 



This form is found near the upper part of the Cincinnati Group. 

 Its range is probably between 600 and 800 feet above low water-mark. 

 It is not common. 



