8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



fore shows pleural grooves and furrows much more strongly than on 

 the exterior. 



Upper Cambrian ; Dead Indian Creek, Clark Fork, Wyoming. 



Holotype. — U.S.N.M. no. 94343. 



DAWSONIA Hartt, 1868 



Dawsonia Hartt, in Dawson, Acadian Geol., 2d ed., p. 655, 1868. 

 Goniodiscus Raymond, Ottawa Nat., vol. 27, p. loi, 1913. 

 Calodisctis Howell, Journ. Pal., vol. 9, no. 3, 224, 1935. 



In the second edition of "Acadian Geology" published in 1868, 

 Dawson, p. 641, quotes Hartt's preliminary report on the first Cam- 

 brian fossils discovered in maritime Canada, which appeared in Bailey's 

 " Observations on the Geology of New Brunswick ", 1865. On page 

 643 Dawson makes the following statement : " other engagements 

 have prevented Mr. Hartt from fulfilling his intention of publishing 

 detailed descriptions of the species. In compliance, however, with my 

 desire to place these interesting forms before geologists in this work, 

 he has kindly communicated to me his ms. notes ; and I have extracted 

 from these the following descriptions of several of the more common 

 species." Then follows descriptions of 26 species, of which 12 are 

 illustrated. 



A figure and description of Microdisciis daivsoui appears on page 

 654. The first paragraph on the following page is written in the first 

 person, but it is not clear whether it was Dawson writing or whether 

 he was merely quoting Hartt. However, a note is appended by Daw- 

 son in the second paragraph which reads as follows : " Mr. Hartt had 

 originally described this species under the new generic name of 

 Dawsonia; but Mr. Billings regards it as a species of Microdiscus of 

 Salter." From this statement it is evident that Hartt described this 

 trilobite as Dazvsonia dazvsoni and that Dawson, without Hartt's direc- 

 tion referred the species to the invalid genus Microdiscus Emmons 

 (not Salter). Consideration of these facts warrants the conclusion 

 that Dazvsonia is a valid genus for this and its related species. Sub- 

 sequently, Dazvsonia was used several times — by Carpenter and by 

 Nicholson in 1873 and by Fritsch by 1879 — ^^"t this does not invalidate 

 its application to a trilobite by Hartt in 1868. 



In 191 3 Raymond reviewed this group of trilobites, proposing 

 Goniodiscus for the species of Dazvsonia. His argument that Dazvsonia 

 could not be restored because meanwhile it had been applied to another 

 animal, is, of course, not well founded, for even if Dazvsonia had 

 been synonymous with Microdiscus when proposed in 1868 its further 

 use in 1873 would not have been allowable. 



