14: Cumings and Mauck — Variation in the 



An inspection of Plates II and III shows the small size of 

 the extreme forms, and conversely the large size and robust 

 growth of those forms near the modes. The largest specimens 

 will not be found exactly at the mode in -any of the characters 

 for which curves are plotted, but in classes to the right of the 

 mode. That is, while it is true, for example, that by far the 

 majority of specimens have three plications in the sinus, the 

 largest specimens are more likely to be found in classes having 

 more than three plications in the sinus. They will never be 

 found in classes having less than three plications. When, how- 

 ever, the class falls some distance to the right of the mode it 

 will again be found to contain small specimens. Smallness of 

 size is, therefore, an accompaniment of the general extinction 

 that prevails more and more, away from the mode. In the 

 case of the number of plications on the valve, extinction does 

 not become severe till the 20th is reached ; and in the classes 

 between 17 and 20 will be found the largest individuals. 



In regard to the validity of the several species or varieties 

 into which the lynx group of forms has been divided, namely, 

 Platystrophia lynx^ P. laticosta, P. dentata Meek {= P. 

 crassa James), there is ahsolutely no character or combination 

 of characters that can be relied upon to separate any large col- 

 lection into distinct species. To a limited extent the above 

 forms differ in range ; although the authors have frequently 

 seen all three represented on a single slab of limestone. It is 

 well, however, to distinguish for stratigraphic purposes such 

 varieties as laticosta. and dentata Meek.^ 



The following is a description of the modal form of Platy- 

 strophia lynx: shell three-tenths wider than long; greatest 

 width about half-way from the hinge line to the front of the 

 shell ; width of sinus seven-tenths greater than its depth ; 

 seventeen angular plications on the ventral valve, three of 

 which are in the sinus ; eighteen on the dorsal valve, four of 

 which are on the fold. 



*As stated in a preceding footnote, the other forms, actitilirata Conrad, 

 hiforata Schl. and other foreign forms of Platystrophia are not considered in 

 this paper. The form identified by Miller, and doubtfully by Meek, as 

 dentata Pander is the costata of the latter author. Pander has figured 

 dentata and costata (= chama Eichwald) side by side on pi. xi of his Beitrage 

 zur Geog. Russ. Dentata has two plications in the sinus and three on the 

 fold, while costata has one in the sinus and two on the fold. The name 

 chama Eichwald cannot be retained for this variety, since the Spirifer cos- 

 tatus of Sowerby is a true Spirifer, and there is no other prior use of the 

 name costata among the Orthidae. See de Yerneuil Geol. de la Eussie, p. 140, 

 and Sowerby, Tr. Geol. Soc. Lond., 2d ser. , v, pi. Iv, fig. 5-7. On the vari- 

 eties of Platystrophia see especially Meek. Pal. Ohio, i, 1873, pp. 112-121 ; 

 Hall, Pal. N. Y., i, 1847, pp. 133-134 ; Winchell and Schuchert, Minn. Geol. 

 Surv., iii, 1893, pp. 454-457; Davidson, British Silurian Brachiopoda, 1871, 

 p. 268 et seq. ; Schuchert, Bull. 87, U. S. G. S., p. 308 ; Sardeson, Am. Geol., 

 xix, p. 109. 



