PJ,ATE XIb—C ontinued. 
Streptorhynchus Ulrichi, sp. 110V. 
Fig-. 15. The interior of a 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, Kentucky. 
Genus DERBY A, Waagen. 
Page 261. 
DeRBYA (?) COSTATULA, Sp. 110V. 
Fig. 16. View from the brachial valve of a small specimen, which shows the characteristic surface orna¬ 
mentation of this species. This consists of strong radial ribs alternating with fascicles of two, 
three or four finer striae. X 2. 
Fig. 17. The cardinal process of a brachial valve similar in external characters to that of the preceding 
specimen. X 3. 
Chester limestone. Crittenden county , Kentucky. 
Genus MEEKELLA, White and St. John. 
Page 26t. 
(See Plate X, figs. 18-23.) 
Meekella occidentalis, Newberry. 
Fig. 18. View of the brachial valve of an internal cast which retains a portion of the shell over me cardinal 
area of the pedicle-valve. The deltidium of this area shows the same structure as in the fol¬ 
lowing species and in the genus Tritlecia, a considerable portion of the coverving between the 
dental ridges being flat or slightly concave, the convex ridge being confined to the middle of 
the plate. The apex of the brachi il 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 extension and convergence of the 
, dental lamellae and the fine 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 striatocostata, Cox. 
(See Plate X, figs. 18-23.) 
Fig. 20. Cardinal view of a large, symmetrical individual, essentially an internal cast in chert; showing 
the position of the dental and crural plates. 
Upper 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 gutta-percha impression of a natural mould. X 3. 
Upper Coal Measures. Lam'ence county, Kansas. 
Genus DERBYA, Waagen. 
Page 261. 
(See Plates X, XI and XIa.) 
Derbya crassa, Meek and Hayden (?). 
(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 Nebrascensis, to which are 
attached several minute pedicle-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 Productus, 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 streptorhynchoid species having 
a median septum in the pedicle-valve, and as Derbya crassa is the most abundant of these forms 
in the associated fauna, the fossils may be tentatively referred to this species. X 10. 
Upper Coal Measures. Near Kansas City, Missouri. 
