GENERA OF THE SUBORDER ORTHOIDEA 



145 



certain forms of Mississippian and Pennsylvanian Schiz- 

 ophorut but differs from them in the degree of devel- 

 opment of these plates. In Orthotkh'ui the dental 

 plates are always high and extend to the front of the 

 muscle area as high ridges. Some Pennsylvanian species 

 of Schizophorui approach Orthot'tch'ui in the accelerated 

 development of the median septum but in them the 

 dental plates have not attained the specialized character 

 of those in Orthotichla. 



Discussion. — The dorsal valve has the general 

 characteristics of the Pennsylvanian Schizofhoria. The 

 posterior adductor scars are situated behind and out- 

 side of the anterior impressions, being separated by a 

 low oblique ridge that is antero-laterally directed. The 

 individual scars are rather elongate, tapering posteriorly 

 but expanded toward the front. This gives the mus- 

 cle-scars a flabellate outline where viewed in the 

 aggregate. It was Derby's idea'** that there were 

 six adductor impressions in the dorsal valve. The 

 smooth spaces on each side of the low median ridge 

 were interpreted as muscle-scars but there is no crenu- 

 lation or any other sign of muscle attachment in the 

 three spaces. Hall and Clarke*" also suggested a third 

 pair of dorsal muscles in Schizofhoria macfarlani. 

 The specimen to which they refer is an old obese shell 

 in the Schuchert Collection. What appear to be lateral 

 muscles are actually pits left by the incomplete cover- 

 ing up of the brachiophore apparatus by adventitious 

 shell. 



Orthotichia structurally forms the passage between 

 Schizofhoria and Enteletes but this does not necessarily 

 mean that the latter actually developed out of Ortho- 

 tichia. Enteletes probably developed directly out of 

 the more plastic Schizofhoria, and Orthotichia may 

 then be a terminal branch of the Schizofhoria line. 



Genus AULACOPHORIA Schuchert and 

 Cooper 1931 



(Gr. aulax, furrow; fhoreein, to bear) 



PI. 29, figs. 2, 5, 10 



Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931, 

 p. 247. 



Genoholotype. — Orthis keyserlingiana De Ko- 

 ninck 1843, Desc. Anim. Foss. Terr. Carb. Belgique, 

 p. 230, pi. 13, fig. 12. 



Description. — Aulacofhoria is proposed for shells 

 having an interior like that of Schizofhoria but having 

 a deep sulcus on the dorsal valve and a strong fold on 

 the ventral one. Besides the genotype, two other 

 European species are placed in this genus, Enteletes 

 injracarbonica Janisevskij from the Lower Carbonifer- 

 ous of the eastern Urals in the vicinity of Khabarny 



"" Bull. Cornell Univ., vol. 1, 1874, p. 30. 

 "'Pal. N. Y., vol. 8, pt. 1, p. 214. 



and E. uralica Gorsky from the Middle Carboniferous 

 of the eastern slope of the Urals. Schizofhoria 

 {Enteletes?) mesoloba Janisevskij may be another 

 form belonging in this genus. 



In the dorsal valve the brachiophore plates are 

 widely divergent as in Schizofhoria and Enteletes, and 

 the sockets are defined by fulcral plates as is usual in 

 the family. In the ventral valve the prominent dental 

 lamellae are subparallel but no prominent median sep- 

 tum was detected, such as occurs in Orthotichia or in 

 Enteletes. The ornamentation is very much like that 

 of Enteletes, much more so than like Schizofhoria. 



Aulacofhoria thus occupies an intermediate position 

 structurally between Enteletes and Schizofhoria. It 

 differs from the former in being less ventricose and 

 inflated and in not possessing the prominent ventral 

 median septum. The great development of the median 

 septum in Enteletes, according to Gorsky, may be an 

 adaptation to the great inflation of the valves to accom- 

 modate the attachment of the adductor or closing 

 muscles. 



Gorsky"* maintains that the type of structure shown 

 by Enteletes injracarbonica Jan. represents the earliest 

 phase of Enteletes. It is our idea, on the other hand, 

 that Aulacofhoria is a terminal offshoot from Schizo- 

 fhoria. We base this conclusion on the greater re- 

 semblance of the interior to Schizofhoria than to 

 Enteletes. 



Subfamily ENTELETIN^ Waagen 1884 



Aberrant, globular or strongly biconvex Schizo- 

 phoriidas that are usually strongly plicate in front, 

 or atavistically ? smooth. 



Geologic range. — Pennsylvanian and Permian. 

 Embraces the following genera: 



Enteletes Fischer de Waldheim 

 Enteletina Schuchert and Cooper 

 Parenteletes King 

 Enteletella Likharev 

 Enteletoides Stuckenberg 



The genetic relations seem to be as shown in 

 Table 15. 



Discussion. — The Enteletinx in their compara- 

 tively short life span have tried to adopt several of the 

 features developed in other groups by more tedious 

 routes of evolution. Parenteletes tried the cella or 

 camera of Mcrista. Enteletella developed a spon- 

 dylium for muscle attachment. Further, there was no 

 stability in the development of the fold and sulcus. 

 This trait is not unusual among the orthids but in the 

 Enteletinx a ventral fold became persistent in two 



'" Bull. Cora. Geol. Leningrad, vol. 43, no. 9, 1927, 

 pp. 1184-1186, pi. 18, fig. 9. 



