PLATE LXm— Continued. 



Gknus ANASTROPHIA, Hall. 



Page ■2'24. 



Anastrophia deflexa, Sowerby. 



Pi^. 28. Profile of a normal aduU example ; showing the surface plication and the predominant convexity 

 of the brachial valve. 



Wenlock limestone. Wenlock Edge, England. 

 Fig. 29. Cardinal view of a specimen which has been transversely sectioned in the umbonal region ; show- 

 ing the supported spondylium of the pedicle (lower) valve, and the septal plates of the bi-achial 

 valve, bearing the crural apophyses. 



Wenlock limestone. Island of ffotland. 



Anastrophia internascens, Hall. 



Fig. 30. Cardinal view of an intei'nal cast, represented with the brachial valve above ; showing the cavi- 

 ties of the septal and socket plates in the brachial valve, and of the spondylium and its 

 median septum in the pedicle-valve. X 2. 



Niagara dolomites. Near Milwaukee, Wiscownn. 



% Anastrophia Verneuili, HmH. 



Figs. 31, 32. Ventral and cardinal views of a large individual; showing the contour and character of the 

 surface plication. 



Pigs. 33, 34. Dorsal and front views of a somewhat smaller specimen with more regularly and sharply 

 plicated sui-face. 



Fig. 35. An enlargement of the interior of the umbonal region of conjoined valves, the pedicle-valve being 

 represented below. In the bra<;hial valve the convei-gent septal plates bear lateral bilobed 

 expansions or flanges, which are the crural apophyses as shown in section, in figure 29. In the 

 pedicle-valve the walls of the supjinrted spondylium are folded over each other in such a man- 

 ner as to form a tubular chamber. This appears to be an abnomial character, as it has been 

 observed in this instance only, but it is nevertheless a natural growth without evidence of 

 break or lesion in the walls of the spondylium. X 2. 



Pig. 36. Similar parts in another specimen in which the spondylium is normally open, but the crural 

 apophyses less perfectly retained than in the shell represented in fig. 35. X 2. 

 Lower Helderberg group. The Helderbergs, New York. 



Fi„'. 37. The interior of a portion of the brachial valve ; showing the cavity of the sessile spondylium or 

 septal plates and the four scars of the adductor muscles. 



Lower Helderberg group. Perry county, Teivnessee. 



Fig. 38. A similar interior with the septal plates and muscular scars more sharply defined ; showing also 

 the false foramen produced by the encroachment of the septal cavity or spondylium upon the 

 beak. 



Lower Helderberg group. The Helderbergs, New York. 



Genus POKAMBONITES, Pander. 



Page -iSi. 

 PORAMBONITES ^QUIKOSTKIS, Schlotheilll. 



Fig. 39. Cardinal view of a specimen showing the cardinal area on each valve and, by translucence, the 



double septa of both valves. X 2. 

 Fig. 40. A portion of the interior of the pedicle-valve; showing cardinal area, delthyrium and teeth. 

 Pig. 41. A similar view of the brachial valve ; showing cardinal area, delthyrial opening and dental 



sockets. 

 Figs. 42, 43. Profile and front views of a ventricose shell ; showing the relative convexity of the valves and 



the development of median fold and sinus. 

 Lower Silurian. liiissia, 



POKAMBONITES OIGA8, Sclimidt. 



Pig. 44. Cai-dinal view of an average specimen ; showing the cardinal area and apical foramen on each 

 valve. By the exfoliation of the shell of the brachial (upper) valve, the bases of the diverg- 

 ent septal plates are exposed. 



Lower Silurian (Lykholmer-Schichten). E.^tland, Russia. 



