CONTRIBUTIONS TO PALEONTOLOGY. 53 



In the dorsal valve, the muscular impressions differ from Meristella ; 

 the hinge-plate is of somewhat different character, and the median septum 

 is scarcely developed. 



The characters of the Genus Merista have been illustrated in a pre- 

 ceding Report.* 



GENUS ^ETZIA (King).! 



In regard to the entire characters and limitations of this genus, 

 there still exists some doubt and difference of opinion among 

 palaeontologists : nor is this difficulty removed by consulting.the 

 published accounts of the genus, and the species referred to it by 

 several authors. 



The genus is described hj Prof. King as follows : 



"A Spiriferidea : in general oval longitudinally; ribbed or 

 " striated ; with large punctures. Large valve foraminated at or 

 " near the apex of the umbone ; with a triangular area. Type 

 " Terebrafula adrieni, De Verneuil. This interesting genus, well 

 " distinguished by the above characters from other Spirife- 

 " RiD^, such as Retzia baylii (^Terehratula id., Davidson), R, 

 " bouchardii ( T. id.^ Dav.), R. oliviani ( T. id.^ De Yern.), and 

 ^^ R. salteri (^T. id.jDAY.), Terebratula feritaj and some other 

 " spirigerous terebratul^eform species, I am strongly disposed 

 " to regard as belonging to the same genus." 



The author remarks : "It appears to be a purely palseozoic 

 genus ; being only found as yet in the Silurian, Devonian, and 

 Carboniferous rocks." 



Mr. Davidson, in the English edition of his Introduction to the Study 

 of the Brachiopoda, does not recognize Eetzia as a distinct genus ; but, 

 referring to it under the Genus Spirigera = Athyris, cites the species 

 which have been placed under Retzia, and expresses an opinion that farther 

 information is required of the internal structure, before the true relations 

 can be determined. 



In the French edition of Mr. Davidson's Introduction, 1856, Retzia 

 is made a subgenus under Athyris, ranking with Merista and Uncites. 



The type of the genus is R. adrieni ( De Verneuil, sp.) ; and the ex- 

 amples cited are R. adrieni, R. serpentina ( de Koninck, sp.), R.ferita 

 (de Buch, sp.), R. esquerra (de Yern. sp.; melonica, Barrande; salteri^ 

 Davidson, etc. etc.). The examples given in the illustrations of the same 

 work, are R. serpentina, R.ferita, R. mucronata, R. adrieni. 



* Thirteenth Report on the State Cabinet, p. 93. 



t Monograph of English Permian Fossils ( Palaeontological Society, 1850, p. 137). 



