CHONETES. 179 



2. CHONETES MABGAKITACEA, Whidborne. Plate XXII, figs. 5, 5 a, 6. 



1896. CHONETES MARGABITACEA, Whidborne. Proc. Geol. Assoc., vol. xiv, 



p. 376. 



Description. Ventral valve small, very transverse, serai-oval. Umbo low, 

 rounded, very slightly extending over hinge. Hinge-line straight, equal to the 

 width of the shell in length, bearing three (or four) nearly perpendicular spines. 

 Margins very gently curved in front, gradually increasing in curvature laterally, 

 and meeting the hinge-line at nearly right angles. Contour of surface moderately 

 convex, becoming flatter on the wings. Ribs about thirty, low, rounded, divided 

 by narrower concave furrows, vanishing on the wings, and crossed by minute 

 regular sharp distant concentric threads, which are twice as close as the ribs. 



Size. Length 7 mm., width 15 mm. 



Localities. In the Porter Collection are six specimens from Roborough, 

 Poleshill, and Pilton; in the Barnstaple Athenaeum one from Bradiford ; in the 

 Museum of Practical Geology one from Braunton ; and in my Collection one from 

 Croyde. 



Remarks. This beautiful shell is distinguishable from Ch. Hardrensis, with 

 which it occurs, by its somewhat larger size, its more transverse and oval shape, 

 and its much larger, fewer, and more simple ribs, as well as by its pronounced 

 concentric ornament. 



From Ch. Phillipsii, Davidson, 1 it differs in its more oval and transverse shape 

 and its considerably finer ornament. 



Ch.pleleia, Schnur, 2 appears to be less transverse, and to have less simple ribs 

 and more oblique hinge-spines. 



3. CHONETES ILLINOISENSIS, Worthen ? Plate XXII, figs. 7, 8. 



? 1858. CHONETES LOGANI, Hall (not Norwood and Pratten). Geol. Eep. Iowa, 



vol. i, pt. 2, p. 598, pi. xii, figs. 1 a e, 2. 

 P 1860. ILLINOISENSIS, Worthen. Trans. St. Louis Acad. Sci., vol. i, 



p. 571. 

 p ]_g68. Meek and Worthen. Geol. Surv. Illin.. vol. iii, 



p. 505, pi. xv, figs. 8 a, b. 

 1896 _ _ Whidborne. Proc. Geol. Assoc., vol. xiv, p. 376. 



Description. Shell rather small, transverse. Hinge-line straight, nearly as 

 long as the width of the shell. Margins moderately convex in front, their 



1 1882, Davidson, ' Brit, Eoss. Brach.,' vol. v, p. 54, pi. iii, figs. 23, 23 a. 



2 1897, Whidborne, ' Quart, Journ. Geol. Soc.,' vol. liii, p. 454, pi. xxxiii, figs. 1, 2. 



A A 



