114 NEW YORK STATE MUSEUM 



referred to R. strigiceps are quite variable in degree of surface stri- 

 ation, yet this species also bears a cardinal area upon the valves. This 

 feature is particularly well shown by a valve from the Taunus quartzite of 

 Katzenloch near Idar in the Rhine province. In the main the specimens 

 of this species are somewhat more finely striated than those from the 

 Presque Isle but this is a difference notable only in the older shells where 

 by obsolescence of the lateral striae the riblets become apparently less. 



An internal cast of R. strigiceps, somewhat distorted, from the 

 Siegen greywacke at the iron mine Alte Mahlscheid near Herdorf illustrates 

 the immature character of certain of the generic structures. Thus the 

 hinge plate and cardinal process are thin and not perforated, the dental 

 plates and pedicle pit rather inconspicuous and the muscular impression not 

 sufficiently strong to eradicate the marks of the shell plications. Such an 

 expression of these structures is immature in the sense that they characterize 

 tH is primary manifestation of species of Rensselaeria. This is their expres- 

 sion, for example, among the species of the Helderbergian fauna. On the 

 other hand the Rensselaerias from Presque Isle stream are in these respects 

 up to the full development of the type of the genus, R. ovoides. These 

 characters in such condition do not therefore indicate a primitive phase nor 

 an early stage in the history of the genus. 



The shells from Edmunds Hill are of more primitive expression, 

 especially in hinge structure, the plate not being thickened though well 

 developed and separated medially or perforated, in this respect having the 

 structure of the early species of the genus, such as occur in abundance in 

 the beds of the Helderbergian of New York. This shell is in a general way 

 smaller and carries within itself the expression of retarded development with 

 reference to the larger forms at Presque Isle. I will not venture the state- 

 ment that the small forms do not occur at Presque Isle but the larger have 

 not been observed at Edmunds Hill. 



The similarity of these smaller forms with the R. stewarti of Dal- 

 housie is very close yet it seems to me improper to unite the shells, for such 

 union would lead to the identification of the still simpler Dalhousie shell 

 with the progressed form from Presque Isle. At Dalhousie the species 

 seems to have become fixed in its primitive details ; conditions in the Chap- 

 man Plantation region have permitted progress beyond the expression of 

 R . stewarti. 



The especial expression of the generic type of Rensselaeria afforded by 

 these two closely allied species is repeated in the shell R . portlandica 

 Billings from the Square Lake limestone of Maine. The last opportunity 

 which the writer had for critical examination of the type of this species 

 was while studying an extensive series of Rensselaeria and brachiopods 

 allied thereto, in the preparation of Palaeontology of New York, volume 8, 

 part 2. It was then observed that the species Terebratula g a u d r y i 



