124 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



European Species 

 Orthis canaliculata Lindstroni 1860 



Distinguishing characters. — Levenea is most 

 like Isorthis in all except cardinalia, but differs in its 

 unequally biconvex or plano-convex lateral profile, and 

 pentagonal ventral muscle field. This genus is close 

 to Isorthis in its ventral interior but differs in hav- 

 ing less widely divergent pallial markings. In the 

 dorsal valve it differs still more strongly from Isorthis 

 in not having a fulcral plate, or as elongate an 

 adductor field. 



Discussion. — Of special interest in Levenea is the 

 remarkable deposition of adventitious shell, especially in 

 the dorsal valve about the various structures of the car- 

 dinalia. Shell matter is laid on the inside surface of 

 the brachiophores and extends around their dorsal face 

 to the wall of the valve. The socket is a deep excava- 

 tion in this adventitious shell and in some specimens 

 may simulate a socket-plate (see pi. 18, figs. 19, 21, 

 29). This support of the brachiophore plates is exactly 

 the same as that seen in Dalmariella s. s. The cardinal 

 process is usually rather small and bilobed, without a 

 pronounced shaft. In old forms a secondary shaft is 

 produced forward over the median ridge. In such 

 specimens the process has the appearance of a fly's head 

 with proboscis protruded. 



This genus is named for Miss Clara Mae LeVene, 

 in recognition of her assistance in the preparation of 

 this monograph: first, by long-continued bibliographic 

 work on the brachiopods, begun in connection with 

 the second edition of Zittel-Eastman in 1913, and 

 carried on to form the basis for the Schuchert-LeVene 

 generic catalogue of 1929; and second, by editorial 

 revision and other work accompanying the transforma- 

 tion of the hand-written manuscript into the present 

 printed volume. 



In the dorsal valve the cardinalia are similar to those 

 of Dalmanella. The brachiophore plates are bladelike, 

 divergent, supported by adventitious shell, which forms 

 a rather thick notothyrial platform. The cardinal 

 process is small, the shaft short, the myophore lobate. 

 The adductor field is somewhat shield-shaped with 

 individual scars subequal. 



Discussion. — Heterorthtna differs from Heterorthis 

 in lacking the widely divergent diductor scars in the 

 ventral valve, and the thickened ridges parallel to the 

 anterior margins. The deposition of adventitious shell 

 about the cardinalia takes more the form of that seen 

 in Dalmanella rather than that of Heterorthis. In the 

 latter the brachiophore plates are thickened at their 

 dorsal and distal extremities, the thickening being pro- 

 longed as curved margins around the adductor field. 

 The cardinal process of Heterorthis is also different 

 from that of Heterorthtna. The myophore of the 

 former is elongated ventrally and the median lobe 

 drawn out posteriorly into a rather sharp carina. The 

 lateral lobes are reduced to small ridges or bosses. In 

 Heterorthina, on the other hand, the process is small, 

 bilobed, and cleft in front, as seen commonly in Dal- 

 manella. No trace of a heterorthoid chilidium was 

 seen in Heterorthina. The internal structure of the 

 genus relates it more closely to Dalmanella than to 

 Heterorthis, and for this reason we are placing it in 

 the family Dalmanellidae. 



Geologic range. — Upper Ordovician of Europe 

 and possibly of the Ohio Valley. 



European Species 



Heterorthina frteculta Bancroft 1928 

 Orthis ellipoides Barrande 1 847 



American Species 

 ? Dalmanella jairmountensis Foerste 1909 



Genus HETERORTHINA Bancroft 1928 



PL 17, figs. 17, 28, 32; pi. 18, figs. 1-8 



Bancroft, Mem. and Proc. Manchester Lit. and Philos. 

 See., vol. 72, 1928, p. 59. 



Genoholotype. — H. frtpculta Bancroft 1928. 



Description. — Externally the shells of this genus 

 resemble Heterorthis in outline, but the dorsal valve, 

 instead of being flat or concave, is very gently convex 

 and bears a shallow sulcus. The surface is rather 

 finely multicostellate. In the ventral valve the teeth 

 are short and flaring and their anterior ends are con- 

 tinued forward as low ridges along the outer margins 

 of the diductor scars. The muscle area is long, extend- 

 ing nearly to the middle of the valve or a little beyond. 

 It is strongly lobate in front, the diductor scars are 

 elongate with subparallel sides, and their anterior ends 

 extend in front of the elongate adductor track. Adjus- 

 ter marks were not seen. 



Family WATTSELLID^ Schuchert and 

 Cooper 1931 



Progressive and terminal Dalmanellacea originating 

 in the Dalmanellida, with subcircular or shield-shaped 

 shells, cordate ventral muscle field, and fulcral plates 

 defining the sockets. 



Geologic range. — Upper Ordovician to Lower 

 Devonian. 



Embraces the following genera: 



Wattsella Bancroft 



Resserella Bancroft 



Horderleyella Bancroft 



M endacella Cooper 



Idiorthis McLearn 



Parmorthis Schuchert and Cooper 



Fascicostella Schuchert and Cooper 



