PLATE XLIX— Continuea. 



Trehatospira Maria, Billings. 



Fig. 21. A dorsal view of the original specimen. 



Lower Helderberg' gi-oiip. Square Lake, Maine. 



Genus RHYNCHOSPIRA, Hall. 



I'age 108. 



Rhynchospira (?) subglobosa, Hall. 



Fig. 22. A dorsal view of an inteinal cast of the conjoined valves ; showing the form of the shell and the 

 impression of the hinge-plate. This is the original specimen and its generic relations are net 

 fully determined. 



Schoharie grit. Schoharie, iV. T. 



Genus TREMATROSPIR.4. Hall 



Page 124 



TrEMATUOSPIRA niBBOSA, Hilll. 



Pigs. 23-26. Doi-sal, ventral, cardinal and frontal views of a large, old and thickened shell ; showing the 



coarse and sharp plication and jiresenting the usual form of the species. 

 Fig. 27. A sinallei' example with the meilian fold and sinus less distinctly developed. 

 Hamilton gi-oup. Yates county, N. T. 



Genus PARAZYGA, gen. nov. 



Page \i7. 



Parazyga hirsuta, Hall. 



Figs. 28-32. Dorsal, ventral, cardinal, frontal and profile views of a normal individual : showing the form, 

 contour' and tine pHcalion of the valves. The sui'face of the shell was covered with short and 

 exceedingly line hair-like .spiiuiles which are retaineil only under the most favorable preserva- 

 tion This is one of the oi'iginal specimens of the species. 



Fig. 33. A preparation, showing, by removal of the brachial valve, the form of the spiral cones and their 

 attachment to the crura. 



Fig. 34. The interior of a pedicle-valve ; showing the character of the muscidar area and the concave del- 

 tidial plates. 



Fig. 35. The interior of a brachial valve ; showing hinge-plate and muscular impressions. 



Fig. 36. A preparation of the braihidium, the pedicle-valve and the upper portion of the spiral cones 

 being removed; showing the mo<le of attachment of the crura and primary lamellEB and the 

 form of the loop. The hinge-plate is not correctly represented. X 2. (c.) 



Fig. 37. The hinge-plate enlarged ; showing its bipartite form and the broad dental sockets. X 3. 



Fig. 38. The interior of the rostral region of the (ledicle-valve from which the m.argioal portion has lieen 

 removed, exposing the short dellhyrial or pedicle tube, and remnants of the teeth and dental 

 plates. X 3. 



Fig. 39. The cardinal portion of the pedicle-valve ; showing the delthyrial tube and the greatly abbrevi- 

 ateil, concave and solid remnants of the dellidial jilates. X 3. 



Hamilton group. Varimis localities in the soft shales of Western New Tm-k. 



Parazyga Deweyi, Hall. 



Figs, 40-42. Dorsal, profile and ventral views ol the original specimen ; showing the form of the shell. In 

 figure 40 the brachial valve is represented as too flat medially, there being a low fold to cor- 

 responil with the sinus on the opposite valve which is shown in fig. 42. 



Fig. 43. The interior of a poitlon of the brachial valve ; showing the form of the hinge-plate and a short 

 median septum. X 3. 



Fig. 44. The same specimen viewed from Ihe cardinal raai'gin ; showing the elevation of the hinge-plate, 

 its recurvature and the loliation of its surface. X 3. 



Fig. 45. The intei-ior of a portion of the pedicle-valve ; showing the concave and solid deltidial plates, 

 coalesced only at fheir anterior mai-t;in, and the recurved teeth. The deltidial plates are con- 

 tinuous with the substance of the shell which fills the entire ro.stral cavity. X 3. 



Fig. 46. A preparation .showing the f(n'm of the spiral <'ones, the jiosition of Ihe loop, the genicnlation of 

 its lateral branches and the shape of the saddle, (c.) 



Lower Helderberg group (Shaly limestone). The Helderhergs, N. T. 



Genus TREMATOSPIRA, Hall. 



Pas:e 121 



Trematospira equistrlata, sp. nov. 



Fig. 47. A dorsal view of an incoiniilele .-hfll. siriulai- m foi m to T. inidtistiiata. but diffeiing fi-imi that 

 species in the regular, equal, I'onnded and unbif urcated surface j)lir;iiions. Those in T. oiiidti- 

 striata are not satisfactorily lepresented in figures 9 and 10, but are sharper and often strongly 

 fasciculal e. 



Lower Helderbei'g group. Cumberland, Maryland. 



