PLATE LXIII— Continued. 



Genus ANASTROPHTA, Ham,. 



Page ■22i. 



Anastrophia deflexa, Sowcrby. 



Kig-. iS. Profile of a normal lulult example ; showing' the surface plication ami the predominant r-,,nvexity 

 of the lirai'hial valve. 



Wenloek limestone. IVeiilock Edc/e, linglancl. 

 Kifj. 29. Cardinal view of a specimen which hiis been transvei-sely sectioneil in the umbonal region ; show- 

 ing' the supporteil spondylimn of the pedicle (lower) valve, and the septal plates of the brachial 

 valve, bi-aring the crui'al apophyses. 



Wenlock limestone. Inland of Gotland. 



Anastrophia internascens, Hiill. 



Fig. 30. Cardinal view of an internal c.ost, r<^pre.■<ented with the brachial valve above ; showing the cavi- 

 ties (if the septal and socket jjlates in the l>rachial valve, and of the spondylium and its 

 median septum in the pedicle-valv<!. X 2. 



Niagara dolomites. Near Milwaukee, JVinronnhi. 



^ Anastrophia Vernkuili, H;itl. 



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

 surface plication. 



Figs. 33, 34. Dorsal and front views of a som<!what smaller specimen witli more regularly and sharply 

 plicated surface. 



Fig. 35. An enlargement of the intei'ior of the umlional region of conjoined vjdves, the pedicle-valve being 

 repi-esented below. In the bi'achial vahe the convergent .septal plates bear lateral bilobed 

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

 pedicle-valve the walls of the supiiorted .spon<lylium are folded over each other in such a man- 

 ner as to form a tubular cluuuber. This apiH^ars to be an abnormal character, as it has heen 

 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. 



Fig. 3li. 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. T/te Helderhergs, New Yarlc. 



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, Tennessee. 



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 vipon the 

 beak. 



Lower Helderberg group. Tlie Helderhergs, iVew York. 



Genus POKAMBONITES, Pander. 



Page -i-jri. 

 PoRAMBONITES .EQUIROSTRIS, .Schlotlu'illl. 



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



di'uble septa of lioth 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 aM<l dental 



sockets. 

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



the development of median fold .and sinus. 

 Lower Silurian. Hassia. 



Porambonites ofgas, Sclimiill. 



Fig. 44. Cardinal 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 basics of the diverg- 

 ent septal plates are exposed. 



Lower Silurian (Lykholmer-Schichten). Estland, Hussia. 



