Notes nil Uirlinwiul mut Rchtlcd Fossils 49 



ceded the other within this group. The IJahi group of Wales 

 and Enghind corresponds approximately to the Mohawkian 

 division among American strata, and in these Mohawkian 

 strata of America species occur which unquestionahly belong 

 to the retrorse division of Dinorthis. Among these is the species 

 collected by Billings (Palaeozoic Fossils, vol. I, 1865, p. 136, 

 figs. Wl a, b) from the Trenton at Ottawa, Belleville, and 

 near TOriginal, in Canada, and also the species figured by 

 Ruedemann (New York State Museum Bulletin, 162, 1912, 

 p. 93, pi. 4, figs. 9-12) from the Snake Hill (Trenton) beds, 

 in Saratoga county, New York. Compared with the type of 

 Orthis retrorsa, these Trenton specimens are much smaller and 

 apparently have a more nearly circular outline. 



Dinorthis carleyi. Hall (Figs. 3 A-E, on plate II of this 

 journal), from the lower or Arnheim member of the Richmond 

 group, in Ohio, Indiana, Kentucky, and Tennessee, also 

 usually is more elongate and more circular in outline than the 

 type of Orthis retrorsa, but not enough specimens of the latter 

 are known to indicate its range of variation in form. The 

 assumption that Dinorthis carleyi eventually will prove dis- 

 tinct from typical Dinorthis retrorsa is based upon the fact 

 that they come from very different horizons. Until the bra- 

 chial valve of Dinorthis retrorsa, from the type locality in 

 Wales, is known, it will be impossible to discriminate the 

 American Richmond forms with any degree of certainty. 



Dinorthis carleyi insolens, Foerstc (Figs. 2 A, B, on plate 

 II), from the base of the upper or Blanchester division of the 

 Waynesville member of the Richmond group, in Ohio and 

 Indiana, is merely a variety tending to have broader and 

 flatter j)lications. 



The brachial vaive (Figs. 3, 3a, 3b, on plate III) erro- 

 neously described and figured by Salter as belonging to Orthis 

 retrorsa evidently is a Hebertella, as already stated. It is num- 

 bered 11213 in the Museum of Practical Geology, in London, 

 and figure IF on plate II of this journal represents a view of 

 a plaster cast of the same specimen, with an attempt to indicate 

 the probable original outline of the valve. Figures IG and IH, 



