BRACHIOPODA. 219 



group are actually punctate. It is not surprising to find some primordial 

 species of Orthis, for example 0. Billingsi (Protobthis), affording indications of 

 a punctated shell, which, with other characters, may be interpreted as showing 

 relationship to Clitambonites and the streptorhynchoids in which a punctate 

 structure is never wanting. 



It should not be forgotten that a grouping of the species of Orthis was made 

 by DE Verneuil in 1845,* and by Quenstedt in 1871.f The very broad concep- 

 tion of generic values which generally prevailed at the date of the former work, 

 but which at the latter period were maintained by few students, renders these 

 groupings of little value in the present state of our knowledge. In de Ver- 

 neuil's classification, based upon thirty-five species and varieties of " Orthis," 

 were two groups of the first order. A, Sinuata, corresponding to King's Schizo- 

 PHORiA, and B, non-Sinuatcc. The latter was divided into a\ striata, b\ plicosa. 

 The striata were again divided, a-, arcuostriata, in which the delthyrium is open, 

 and b'-, rectostriata, in which the delthyrium is closed. The former of these 

 included the a', uniarea, with a rudimentary area on the brachial valve (ex. 

 0. elegans, Bouchard), and' b% biarea, with areas developed on both valves. Of 

 the biarea were two subdivisions, a.\ filiarea (ex. 0. Michelini = RmFWO- 

 MELLA ; 0. tetragona = Schizophoria) ; h\ ekgantula (ex. O. elegantula, 0. parva 

 = Dalmanella). Of b", rectostriata, were also the subdivisions a;'',umarea, and b'^ 

 biarea, and of the former of these two groups a\ with three or more secondary 

 striae in the furrows (= Orthothetes) ; b', with but one or two such striae 

 (=:Meekella, Streptorhynchus, Derby a, Orthothetes); of the latter, biarea, 

 were a\ Gonambonites (^Clitambonites), and b*, Pronites (= Clitambonites 

 and Orthisina). The b', plicosa, were divided into those with simple plications 

 (0. calligramma), and those with dichotomous plications (0. extensa, Pander). 



Quenstedt instituted three principal divisions of his ortuid^: (1) ventriplexa, 

 with convex pedicle-valve ; (2) ventricava or expansa, with concave pedicle-valve ; 

 (3) dorsicava, with concave brachial valve. Representatives of the first in- 

 clude Schizophoria, Porambonites, Orthisina, Clitambonites, Streptorhynchus, 



* Geol. Russ. et des mont. de I'Ural. 



f Petrefactenkunde Deutschlands: Brachiopoden. 



