38-4 MISSISSIPPIAN BRACHIOPODA 



shell in the exceedingly elongate dental lamellae, the very shallow mesial 

 sinus and in the solid covering of the delthyrium by a pseudo-deltidium. 

 The type specimen is an internal cast in chert, with the external mould, 

 so that both the internal and external characters can be clearly seen. 

 The internal cast shows an entire absence of any delthyrial plate such as 

 is present in Pseudosyrinx and Syringotliyris, joining the dental lamellae 

 transversely. The pseudo-deltidium is strong and rigid, and has not 

 been destroyed in the least by f ossilization ; in the genus Spirifer this plate 

 is exceedingly delicate and is rarely or never preserved, in Syringothyris and 

 Pseudosyrinx it is more commonly present, but is always a thin, delicate 

 plate which is much crumpled and crushed in fossilization when it is 

 preserved at all, but in this species it was apparently as rigid and firm 

 as any part of the shell. The absence of a foramen through the pseudo- 

 deltidium is not an uncommon feature in Cyrtia. The absence of a punc- 

 tate shell structure cannot be safely affirmed for the species from the 

 observation of a single specimen, but in this example there is not the slight- 

 est indication of it. The combination of characters present in the speci- 

 men seems to indicate only the genus Cyrtia, to which genus the specimen 

 is referred. 

 Horizon. Residual chert, probably of Keokuk age. 



Genus SYRINGOTHYRIS Winchell 



Description. Shells varying in size from small to very large, spiriferoid 

 in form', with a much elevated cardinal area, the hinge-line straight and 

 elongate, representing the greatest width of the shell, the fold and sinus 

 well developed and usually non-plicate. The pedicle valve subsemi- 

 pyramidal in form, the high cardinal area either flat, concave or convex, 

 differentiated into three regions, a central including the delthyrium, and 

 two lateral, by a pair of lines originating at the apex and passing 

 obliquely to the cardinal margin, which they intersect at equal distances 

 from the basal angles of the delthyrium; the central region is distinctly 

 marked by vertical stria?, while the lateral regions are marked only by 

 the horizontal lines of growth ; internally the dental lamellae are mod- 

 erately well developed, they rest upon the floor of the valve and are a 

 little produced anteriorly along the lateral margins of the muscular 

 scar; they are united transversely by a delthyrial plate whose position is 

 subparallel with the cardinal area but somewhat depressed below it ; 

 this plate extends to various distances from the apex of the delthyrium 

 towards the hinge-line and at the middle point of its cardinal margin it is 

 produced still further towards the cardinal margin of the valve as a free 

 spine-like process ; on the inner side of the spine-like extension of the 

 delthyrial plate, and continuing along the median line of the inner 

 surface of the plate towards the apex of the. valve, is a tube which is 



