PLATE 5 



Figs. Eridorthis rogersensis Foerste 



1, 5. — Dorsal exteriors, showing fold. In early stages the 

 dorsal valve bears a sulcus which later reverses and 

 becomes a fold. 



Ordovician (Trenton, Cynthiana), Rogers Gap, Ky. 



Cat. No. 78712, U. S. Nat. Mus. x 1.5. 



Eridorthis aff. E. nicklesi Foerste 

 2. — Ventral internal mold, showing Orthis-Wke muscula- 

 ture, pallial trunks, and low median rib. 

 Ordovician (Eden, Fulton), New Richmond, Ohio. 

 Cat. No. S 2102. x 2. 



Eridorthis nicklesi Foerste 

 9. — Ventral valve, showing depression of fold to form a 

 sulcus at front of valve. 

 Ordovician (Trenton, Cynthiana), Rogers Gap, 

 Ky. Cat. No. 7871 1 U. S. Nat. Mus. x 1.5. 



Glyptorthis fausta (Foerste) 



4. — Dorsal interior, showing H esferorthis-\\k& cardinalia. 

 7. — Ventral interior, illustrating musculature of the genus. 



Silurian (Brassfield), near Dayton, Ohio. Cat. No. 



S236. xl.5. 



8. — Dorsal exterior, showing incipient sulcus at posterior. 

 Silurian (Brassfield), Centerville, Ohio. Cat. No. 

 S238. xl.5. 



Figs. Schizoramma fasciata (Hall) — Cont. 



This genus has been described as a subgenus of 

 Orthostrofhia, but from its internal structure is dis- 

 tinct enough to merit generic ranic. Schizoramma 

 does not have the small, confined ventral muscle area 

 and the elevated adductor impressions of the other 

 genus. 



Dolerorthis rustica osiliensis (Schrenk) 



10, 12, 19,21. — Lateral, posterior, dorsal, and ventral views 

 of exterior, fig. 1 showing faint concavity of ventral 

 valve toward the front. 

 15. — Dorsal interior, showing orthoid brachiophores and 

 cardinal process, and notothyrial platform. 

 Silurian (Gotlandian), Gotland, Sweden. Cat. No. 

 S282. xl.5. 

 20. — Ventral interior, showing closely apposed pallial trunks 

 separated by a low septum that forks at the front. 

 Subreniform ovarian impressions bounded by these 

 sinuses. Compare with Orthis s. s., Hesferorthis, and 

 Glyftorthis (pi. 2, fig. 18; pi. 4, fig. 27; pi. 6, 

 fig. 26). 

 23. — Dorsal interior, showing median ridge, orthoid cardi- 

 nalia, large posterior adductor scars, and smaller bipar- 

 tite anterior adductor impressions. Cf. fig. 24. 

 Silurian (Wenlock), England. Mus. Comp. Zool., 

 Harvard Coll. x 1.5. 



Schizoramma ? gotlandica Schuchert and Cooper, n. sp. 

 3, 6. — Dorsal and ventral exteriors. 



Silurian (Gotlandian), Gotland, Sweden. Cotypes. 



Cat. No. S 228. xl.5. 



Schizoramma rjisis (Hall and Whitfield) 



11, 16. — Ventral and dorsal exteriors of a silicified speci- 

 men, showing ornamentation. 

 Silurian (Niagaran, Meniscus) , W. Tennessee. Cat. 

 No. S221. Fig. 11 X 1.5; fig. 16 x2. 



Schizoramma fasciata (Hall) 



13. — Ventral interior, somewhat crushed, showing orthoid 

 musculature, and, more indistinctly, the two closely 

 apposed palli-il trunks. 

 14. — Dorsal interior, to show orthoid brachiophores; low, 

 broad, median ridge; simple cardinal process; and 

 accessory ridges on each side of it. Small adductor 

 impressions more indistinctly visible. 

 Silurian (Clinton), Osgood, Ind. Cat. No. S 222. 

 X 1.5. 



Dolerorthis jnterplicata (Foerste) 



18. — Dorsal interior, showing characteristic cardinalia. 

 Silurian (Niagaran, Osgood), Osgood, Ind. 

 No. 8 279. X 1.5. 



Cat. 



Dolerorthis flabellites (Foerste) 



1 7, 24. — Obese dorsal interiors, illustrating interesting old- 

 age modifications of cardinalia and notothyrial plat- 

 form, and brachiophores heavily overgrown with ad- 

 ventitious shell substance, which hides them almost 

 completely. Note "orthoid" ribbing of internal mar- 

 gin. In fig. 24, note especially adductor impressions 

 and compare with fig. 23. Compare fig. 24 with 

 fig. 8 of pi. 1. 



22. — Ventral interior, showing orthoid musculature, and 

 pallial sinuses bounding subreniform ovarian impres- 

 sions. Cf. fig. 20, and ventral interiors of Orthis, 

 Hesferorthis, and Ghftorthis. 

 Silurian (Niagaran, Osgood), Osgood, Ind. Cat. 

 No. S272. xl.5. 



204 



