NEW OSTRACODERM— 0RVIG 5 



skeletal plates and scales, more or less fragmentary; however, no 

 single specimen shows any of these elements in their natural associa- 

 tion. The average size of the plates and scales is somewhat larger 

 than that in the Harding Sandstone of Colorado and the sandstone 

 and shale of the Winnipeg formation of the Williston Basin in Mon- 

 tana, and very small elements are missing altogether, a circumstance 

 which probably indicates that the material has been sorted mechani- 

 cally (by cmTents, etc.) prior to fossilization. The plates and scales 

 have been abraded by rolling to some extent, but cannot, nevertheless, 

 have been transj^orted very far from their place of origin. 



The state of preservation of the material is unusually favorable 

 both for macroscopial and microscopical investigation. The plates 

 and scales are easily freed of adhering sand-grains, e. g., by means of 

 a sharp needle-scalpel, and the thin coat of reddish iron oxides which 

 frequenth^ obscures the fine details of their ornamentation can be 

 removed, either with sodium hexametaphosphatc or by boiling, for 

 a very short time only, in a 10 percent solution of potassium hydrox- 

 ide. The histological structure of the hard tissues is excellently dis- 

 played in those specimens which are light yellowish in color, but it 

 has become obscured to some extent in those which are impregnated 

 with iron oxides. For the preparation of exactly orientated thin sec- 

 tions, it is advantageous to embed the specimens in thin rods of 

 acrylatic plastic by means of a bakelite press, according to the method 

 recentlj^ described by the writer (0rvig, 1957, p. 370). 



The exoskeletal plates figured on plate 2, figm-es 1-3, and plate 3, 

 figures 1-4, are from the gray, fissile shale of the Winnipeg formation 

 of the Williston Basin (see, e. g., Ehlers, 1943, p. 1620; McCabe, 1954, 

 p. 1998, fig. 10) contained in the drill core material from eastern 

 Montana at my disposal. In this shale, which also exhibits phos- 

 phatic nodules, various invertebrate fossils such as lingulid shells, 

 etc., and conodonts, the vertebrate remains are dark brownish or 

 black. Their histological structure is frequently well preserved but 

 is, in places, obscured by post-mortem changes caused by penetrative 

 Algae or Fungi (see, e. g., Peyer, 1945; Bj^strow, 1956). 



It is worth mentioning here, finally, that the plates and scales of 

 the Harding Sandstone — whose ornamentation is, in many cases, 

 difficult to bring out satisfactorily by the ordinary methods of me- 

 chanical preparation — can be studied to great advantage on latex 

 micro-moulds made from the impressions in the rock after the re- 

 moval of the hard tissues with hydrochloric acid. A perfect repro- 

 duction of even very minute details of the ornamentation of those 

 elements can be obtained by the method (described by Bahd, 1955, 

 p. 202; see also Gill, Caster, and Boswell, 1956, p. 198) of treating the 

 etched surface of the sandstone with liquid detergent (e. g., Johnson 



