PLATE XI A— Coiilinac'l- 

 Fifj II. All internal cast of the, brachial valve. 



Fig. 12. The canlinal lu-ocess, enlai'^red. The lolies aie strongly detineil, the crural jilates shoit and 

 slightly recurving where they join the bottom of the valve, producing a thickening of the den- 

 tal sockets. X 3. 



Lower Helderberg group. Albany county. N. Y. 



0UTII0T1IETE.'< PKAVA, Ililll. 



Fig. 13. The interior of a brachial valve retaining the cardinal process, flabellate muscular scai's and traces 

 of vascular sinuses. 



Upper Devonian. Hackherry Ghove, Iowa. 



OkTHOTHKTES rHKMtjN(?ENSIS, C'oinail. 

 (See Plate X, tig. 9.) 

 Fig. 14. The cardinal proces*!, enlarged; showing upon its summit the edges of the lolies on the jiosterior 

 face. The transverse grooves at the junction of the process with the crural plates are made to 

 appeal- somewhat too abrupt. Fiequently the lobes of the cardinal pi-ocess are moi'e deeply 

 divided than in this specimen. X 2^. 



Hamilton grouji. Western iVcic York. 

 For further illustration, see Palawntology of New York. VoluiLie IV, plates ix and x. 



Orthothetes cuenistkia, (Pliilliii.- ?j Mi'uk. 



Fig. 1,^). The cardinal process, enlarge<l ; showing the character of its iimei' surface and the extent of the 

 crural plates. X 3. 



Waverly group. Sciotoville, Ohio. 

 For other illusti'ation, see Palteontologj' of Ohio. Volume II, plate x, tig. 5. 



Okthothete8 lens, AVhite. 



Fig. 16. The exterior of a jiedicle-valve. 



Fig. 17. The interior of the same valve ; showing area, deltidiuni. teeth and nuiscular impressions. 



Fig. 18. The extei'ior of a brachial valve. 



Fig. 19. The interior of the same valve; showing cai'dinal process, muscular impressions and ov.irian 

 markings. 



Fig. 20. The cardinal process of the same specimen, enlarged to show its structure. Its outer face is cov- 

 ered t)y th(! deltidiuni, which conforms to the grooved surface of the lobes. The crural plates 

 are strongly I'ecurved at their bases about the dental sockets. X 3. 

 Choteau limestone. Louisiana, Missimri. 



Fig. 21. A very young pedicle-valve which retains the perforation at the apex of the deltidiuni. X 8. 



Fig, 22. Cardinal view of the same sjiecimen ; showing the height of the area and the jirominence of the 

 deltidiuni. X 8. 



Choteau limestone, PiAre county, Missouri.. 



Genus DEKBYA, Waagen, 



(See Plates X. XI and XIn.) 

 P.lRC 261. 



Derbya Hkoadheadi, sp. IIOV. 



Fig. 23. Cardinal view of an entire, mature individual ; showing the rugose and soniewhal irregular ped- 

 icle-valve, the more symmetrical brachial valve bearing a median sinus. 

 Fig. 24. Profile view of the same specimen. 



Upper Coal Measures. Kansa.^ City, M'lssouri. 



DeKBYA RUGINOSA, ti[). IIOV. 



Figs. 2,5, 2I>, 27. 'ITiree views of an internal cast in chert, retaining portions of the inner laminae of the 

 shell. Both valves were of in egular growth, the brachial valve not having the median sinus 

 of the pre<-eding species. There are many jioints of similnrily between this fossil and the 

 Orthis senilis, VhWWits (Streptorliyvc?tus crtnislria. var. senilis, David.soii), which has been shown 

 by Dkbbv to have a septum in the pedicle-valve. 



Keokuk limestone. New Providence, Indiana. 



