GENERA OF THE SUBORDER ORTHOIDEA 



143 



Genus SCHIZOPHORIA King 1850 



PI. 23, figs. 11, 16-18, 20-25; t. fig. 12 



King, Mon. Perm. Foss., 1850, pp. 105, 106. 



Genoholotype. — Conchylioitthus Anomites resu- 

 ftTMtus Martin 1809, Petref. Derb., pi. 49, figs. 13, 

 14. 



Description. Exterior. — Externally like Hebert- 

 ella; margins rounded, cardinal extremities rounded, 

 hinge-line usually narrower than the greatest width 

 of the shell; lateral profile resupinate, convexity of 

 valves varying, the dorsal valve always with the greater 

 convexity; anterior commissure rectimarginate to uni- 

 plicate; dorsal valve frequently with a low fold; 

 ventral valve frequently sulcate in front; ventral palin- 

 trope the longer, faintly or strongly apsacline, curved 

 or plane, beak slightly or strongly incurved, umbo 

 gently or strongly convex; dorsal palintrope short, 

 curved, very strongly apsacline so that it overhangs 

 the ventral interarea; multicostellate, with abundant 

 hollow costella;; test fibrous, punctate. 



Ventral interior. — Delthyrial cavity usually deep; 

 teeth strong; crural fossettes oblique; dental plates 

 strong, frequently obscured by adventitious deposit, 

 extended about the margins of the muscle area as a low 

 ridge; muscle area bilobate or obcordate; diductor 

 scars long, divergent, separated by a wide or narrow 

 ridge having its origin a short distance forward of 

 the apex; adductors small, borne on the median 

 ridge; adjustor impressions usually long and tenuous, 

 situated on the outside margins of the diductors. 



Dorsal interior. — Cardinalia large; brachiophores 

 scarcely separable from their supporting plates, vertical, 

 or nearly so, strongly divergent, continued forward 

 slightly as a ridge along the lateral margins of the mus- 

 cle field; cardinal process in young shells like that of 

 Rhipidomella, but in old shells largely resorbed, mak- 

 ing a narrow ridge. In old shells an elevation is fre- 

 quently formed on each side of the cardinal process in 

 the notothyrial cavity. Muscle area quadripartite, the 

 anterior pair of diductors being separated from the 

 posterior pair by oblique ridges extending antero-later- 

 ally from the median ridge; peripheral margins thick- 

 ened and elevated in some species. Pallial sinuses 

 prominent, six in number, four of these taking their 

 origin at the anterior extremity of the median ridge, 

 starting as two trunks, then dividing into four and 

 extending anteriorly in a subparallel arrangement, re- 

 peatedly branching near the anterior margin into sub- 

 sidiary rami. Two other trunks originate, in some 

 species, at the end of the ridge dividing the adductors, 

 passing antero-laterally, bifurcating near the margin 

 and then becoming arborescent at the margin. 



Geologic range. — Silurian (Clinton) to Pennsyl- 

 vanian, with a very wide geographic distribution. 



American Species 



Schizofhoria chouteauensis Wcllcr 1914 



S. cora (D'Orbigny) 1 842 



S. ftoydeusis Bclanski 1927 



S.iotvensis (Hall) 1858 



S. iotvensis magna Fenton and Fcnton 1924 



S.macjarlani {Meek) 1868 



S.multislriata (Hall) 1857 



S. oriskania Schuchcrt 1913 



S. foststrhtula Wcllcr 1914 



S. />r»Vw Stauffcr 1918 



S. resufinoitles (Cox) 1857 



5. sedalie?tsis Wellcr 1914 



5. senecta Hall and Clarke 1 892 



S. j/r«a/tt/d (Schlothcim) 1813 



S.striatula tnarylanJ tea Clarke and Swartz 1913 



S.swallovi (Hall) 1858 



5. /«//«'<;««/ (Vanuxem) 1842 



Rhifidomella iubelliftica (White and Whitfield) 1 862 



Foreign Species 



Schizofhoria beaumonti (Verneuil) 1849-1850 



S.fragilis Kozlowski 1929 



S. injracarbonica Janisevskij 1911 



S. interstriata Janisevskij 1911 



S. frovulvaria (Maurer) 



S. resufinaia {MiiUn) 1809 



S. resupinata lata Demanet 192 1-1923 



S. resupinata rotundata Demanet 1921-1923 



5. striatula (Schlotheim) 1813 



S. fw/fijrw (Schlotheim) 1820 



Distinguishing characters. — Schizophoria is 

 distinguished by its convexo-concave profile, the diver- 

 gent or subparallel diductor scars in the ventral valve 

 separated by a low median ridge (euseptoid) which 

 bears the adductor marks, and in the dorsal valve by 

 the widely divergent crural apparatus, characteristic 

 muscle marks, and pallial trunks. The adductor mus- 

 cles are separated by a curved, oblique ridge, a feature 

 which at once separates this genus from Proschizo- 

 phoria. The pallial marks consist of four or six sub- 

 parallel trunks. Schizophoria closely resembles Hebert- 

 ella externally, but the fundamental difference in shell 

 structure and cardinalia serves to differentiate them 

 immediately. The similarities and differences between 

 Orthotichia and the genus under discussion are pointed 

 out under the former genus. 



Discussion. — Schizophoria is a long-ranging genus 

 and for this reason shows considerable variation in its 

 internal anatomy. In the ventral valve the variation 

 is seen in the musculature and the dental plates. The 

 diductor scars vary from subparallel and extremely 

 elongate in some species (S. vulvaria and S. beaumonti, 

 Lower Devonian of Germany) to widely divergent 

 and large or small (5. propinqua, S. provulvaria, and 

 S. niultistriata). In S. iowensis the muscle area is 

 obcordate and much like that of Hebertella. Occa- 

 sionally the adjustor scars are considerably developed, 



