PI-ATE XlB— Coiitimieil. 



Stkeptorhynchus Ulriciu, sp. IIOV. 



I'^iff. 15. Tlu- interior of ii pedicle-valve, referred to the genus on account of the peculiar form of the shell 

 and the absence of median septum or dental plates. 



Chester limestone. Crittenden county. Kmitucky. 



Genus DERBYA, Waagen. 



P;ige 2()i. 

 DeKBYA (?) COSTATULA, Sp. IIOV. 



Fiff. 16. View from the brachial valve of a small specimen, which shows the characteristic sin-face oi'iia- 

 mentalion of this species. This consists of strong radial rilis alternating with fascicles of two, 

 three or four finer strias. X 2. 



Fig. 17. The cai'dinal process of a brachial valve similar in external characters to that of the prec^eding 

 specimen. X 3. 



Chester limestone. Crittenden county, Kentucky. 



Genus MEEKELLA, White and St. John. 



Page 264. 

 (See Plate X, figs. 18-23. j 



Meekella occidentalis, Nowbcny. 



Fig. 18. View of the brachial valve of an internal cast which retains a portion of the .shell over tne cardinal 

 area of the pedicle-valve. The deltidium of this area shows the same structure as in the fol- 

 lowing species an'd in the genus TmrLEci.i, a considerable poi'tion of the covei'ving between the 

 dental ridges being flat or slightly concave, the convex I'iilge being confined to the middle of 

 the plate. The apex of the brachi d valve is I'emoved, showing (imperfectly in the figure) the 

 basal ])ortion of the inner sui'face of the cai'dinal process. 



Fig. 19. An incomplete internal cast of the pedicle-valve; .showing the extension and convergence of the 

 dental lamelliE and the tine radial lines upon the surface of the plications. 

 Both figures are from the original specimen of Orthisina occidentalis, Newberry. 

 Upper Carboniferous limestone. Canon of Diamond River. 



Meekella stkiatocostata, Co.x, 

 (See Plate X, figs. lS-23.) 

 Fig. 20. Cardinal view of a large, symmetrical individual, essentially an internal cast in chei-t ; showing 

 the position of the <lental and crural plates. 



Upper Coal Measures. Winterset, lovM. 

 Fig. 21. Cardinal view of a distorted specimen, with an unusually high cardinal area. 

 Fig. 22. The form of the cardinal process, from a gutta-percha impression of a natural mould. X 3. 

 Upper Coal Measures. Lawrence county, Kansas, 



Genus DERBYA, Waagen. 



Page 261. 

 (See Plates X. XI and XI.\.) 

 Dekbya crassa, Meek iuul Htiydeii (?). 

 (See Plate X, figs. 10. 11 ; and Plate XIa, figs. 28-33.) 

 Fig. 23. A portion of the internal surface of the brachial valve of Productus Nebrasceiuiis, to which are 

 attached several minute pedicle-valves, some of which sKow the presence of a broad cardinal 

 area, deltidium an<i a median seiituin. It will be observed that most of the attached shells 

 have their hinge-lines par.allel to that of the Productu.s, though their relative positions are in- 

 verted. X 3. 

 Fig. 24. A further enlargement of three of these shells ; showing all the details of structure that are re- 

 tained. These attached valves seem to be the young of some streptoi-hynchoid species having 

 a median septum in the peilicle- valve, and as Derhya cra.^sa is the most abund.-mt of these foi-ms 

 in the associated fauna, the fossils may be tentatively i-eferred to this species. X 10. 

 Upper Coal Measures. Near Kansas City, Missouri. 



