118 



actors hold tlii'()u,ij:liont the life history of an individual. I'rosser was the 

 first to refer this shell to Derhya.'r'i 



On referring to de Koninck's figure of his Orthix iimhraculum Schlot- 

 heim|||j the striking similarity will at once be apparent and by compariug 

 this figure and description with that of Bronn,§§ of the Eiffel Devonian 

 (apparejitly after examining the types), the difference between the typical 

 O. iu)ibt~ac 111 Kill and de Koninck's si>ecinien, and the similaritj' of the latter 

 with the American species at once becomes apparent. Koninck's description 

 gives his species 108-109 striae and if this is true, it is hardly identical 

 with the American species as this (and de Koninck's figure) give 160 to 

 2U0 on a specimen of the same size. As to the question of the name of the 

 American species, it is distinct from O. ninbraculum and Meek's term will 

 take precedence for the American form. If they are identical, as seems 

 probable, it will also apply to de Koninck's shell. 



On comparison of typical specimens of this shell with the descrii)tion 

 and figures of Hall and Clarke's Derhj/a ciiiiihuUi it will be seen that they 

 are all identical. This duplication is due to a habit of Mr. Meek's of 

 describing a species under one term, then at the close of the description 

 .stating that in all i)r<)bahility it does not belong to the species referred to 

 but is probably a new species, then proposing the name at the end of the 

 whol(> description.* 



(>ne of the specimens obtained was fortunately covered with young 

 specimens of whose relation there can be no doubt as Deihiiu niiiltistriata 

 is the only Derbya in this horizon at Torrence where these specimens were 

 found. The smallest specimen measured a trifle over 1 nun. wide. In a 

 specimen 5 mm. wide the mesial septum is well developed. 



The high cardinal area is well illustrated by the measurements of a 

 small siiecimen. The pedicle valve length was ]i/4mni. and width ."> mm. 

 The cardinal area \A'as nearly square and measured 3 nun. x 2 mm., or larger 

 than the pedicle valve. At no time in its develojimcnt was it seen to have 

 a form identical with the tyiiical adult I), cnis.sa. 



tfKansas River Section of the Permian and Pernio-C^arboniferous Rocks of Kansas. 

 Bull. Geol. Soc. Anier., VI, p. 40, 1894. 



!l II Description des Animaux Fossiles de Koninck, pp. 222-224 and PI. XIII. fig:. 4h. b. c 

 et fig. 7, a, b, c, et PI. XIII bis. tig. 7. a, b. 



?§Lethaea Geoyrnostica Bronti, pp. 368-H63 and PI. H', i\g. 11, h. h, c. 



*Pal. N. Y.. Vol. VIII. r^t. I, page 348 PI. lib. fig. 2-3. 



