BRACHIOPODA. Ill 



To Rhynchospira are to be referred, primarily the Lower Helderberg species, 

 Waldheimid formosa, W. globosa, and W. redirostra. Hall. It is also probable that 

 the Retzia Eledra, Billings, of the Square Lake, Maine, fauna, and the Retzia 

 Eugenia, Billings, of the Hamilton group, belong to the same genus. Whether 

 the species of the Waverly fauna here described as Rhynchospira scansa, sp. nov., 

 is a true Rhynchospira, cannot be determined from the material at hand. 



A very considerable number of species from the American palaeozoic faunas 

 have been referred to Retzia, and of several of these it has been impossible to 

 obtain representatives for examination Some of the specific names current 

 are unquestionably synonyms for earlier terms, but after the elimination from 

 the list, of species which may confidently be referred to some of the various 

 genera of retzioids here discussed, there will still remain some whose internal 

 structure is too imperfectly known to permit a discriminating reference. With 

 regard to the so-called Retzias of the British and European Devonian and 

 Silurian, it is hardly proper in this place to e.xpress more than the opinion 

 that farther careful investigation of these shells is necessary to their correct 

 generic classification. 



In the development of the fauna of the Niagara group, at Waldron, Indiana, and 

 southward, there is a very abundant species, Rhynchospira evax, Hall, 1863, which, 

 in specific features, is closely related to the Atrypa aprinis, (de Verneuil) Hall 

 (=Retzia apriniformis, Hall, 1859), of the Niagara fauna of New York, and gener- 

 ically to the later typical forms of Rhynchospira, though presenting some 

 diflferences worthy of note. The hinge-plate has no posterior extension, 

 but its anterior lobes are greatly developed into long, divergent crural bases. 

 They are separated to the apex of the beak as in Parazyga hirsuta, and between 

 them lies a small linear cardinal process. There is also a stout median septum 

 in this valve, whose height is equal to nearly one-half the depth of the valve. 

 The loop has a more acute stem and its lateral branches are of the same width 

 from their origin to the point of union. It is also frequently the case in this 

 species that the deltidial plates remain distinct and uncoalesced at maturity. 

 These differences from the typical Rhynchospira are perhaps such as belong to 

 an inceptive stage in the development of the genus, but it will serve a good 



