I"I,ATE XlB— Contimieil. 



Stueptokiivnctius Ur-RICHt, .sp. IIOV. 



b'ig-. 1'). The iiiterioi- of ii pediclo-valve, i-fft-i-red to the gtnius on account of the peculiar form of the shell 

 anil the absence of nieilian septum or dental plates. 



Chester limestone. Crittenden county, Kentucky. 



Genus DERBY A. Waagen". 



P:lgc 281. 



DeUBYA (?) COSTATULA, Sp. IIOV. 



Fiff. IB. View from the I ira«:lii:il valve of a small specimen, which shows the characteristic surface orna- 

 mentation of this species. This consists of strong radial ribs alternatin-f with fascicles of two, 

 three or four finer strias. X 2. 



Fig. 17. The cardinal process of a brachial valve .similar in external characters to that of the prei-eiliuff 

 specimen. X 3. 



Chester limestone. Orittenden county, Kentucky. 



Genus MEEKELLA. \Vhite and St. John. 



Page 26t. 



(See Plate X, fis^.s. 18-23.; 



Meekella occidentalls, Newberry. 



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 deltidiuin of this area shows the same struc-ture as in the fol- 

 lowing species and in the genus Tripleita, a considerable portion of the coverving between the 

 dental ridges being flat or slightly concave, the convex riilge being conlineil to the middle of 

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

 basal portion of the inner surface of the cardinal process. 



Fig. 19. An incomplete internal cast of the pedicle-valve; showing the exten.sion and convei-gence of the 

 dental lamellse and tlie tine radial lines upon the surface of the plications. 

 Both figures are fi-om the original specimen of Orthisina occidentals. Newberry. 

 Upper Carboniferous limestone. Canon of Diamond River. 



Meekella striatocostata, Cox. 



(See Plate X. figs. lS-2.3.) 

 Fig. 20. Cardinal view of a large, symmetrical individual, essentially an intei'iial cast in chert ; showing 

 the position of the dental and criu'al plates. 



Uppei' Coal Measures. Winterset, Iowa. 

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

 Fig. 22. The form of the cardinal process, from a gntta-pei'cha impression of a natural mould. X 3. 



Upper Coal Measures. Lawrence county. Kansas. 



Genus DERBYA, Waagen. 



Page 261. 

 (See Plates X, XI and XIa.) 



Dekbya crassa, Meek and Haydeii (?). 

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

 Fig. 23. A portion of the internal surface of the lirachial valve of Productus NebrasceiwiL's, to which are 

 attached sever.al minute jiedicle-valves, some of which show the presence of a broad cardinal 

 area, deltidium and a median septum. It will be observed that most of the attached shells 

 have their hinge-lines parallel to that of the Proddctu.s, though their relative positions ai-e in- 

 verted. X 3. 

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

 tained. These attached valves seem to be the young of some strepforhynchoid spet-ies having 

 a median septum in the jiedicle-valve, and as Derhya cra.ssa is the most abimdant of tliese forms 

 in the associated fauna, the fossils may be tentatively referred to tliis species. X 10. 

 Upper Coal Measures. jVear Kansas City. Mis-wuri. 



