132 



GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



actually punctate. Mystrofhora, however, differs so 

 strongly from Skenidium in other details that it could 

 easily have been determined as generically distinct with- 

 out the aid of punctation. The lobate cardinal process, 

 together with the punctation, at once establishes 

 Mystro-phora as a dalmanellid. It differs further from 

 Skenidium in the ventral valve, which has no spondy- 

 lium; instead, the divergent dental plates are attached 

 directly to the floor of the valve. In the apex, grow- 

 ing to the inner sides of the dental plates, is a flat plate, 

 probably for pedicle attachment, similar to that seen 

 occasionally in Schizofhoria and other members of the 

 Schizophoriidas. 



Discussion. — In describing Mystrofhora, Kayser 

 did not definitely designate a genotype. Underneath 



Fig. 21. — Mystrofhora areola (Quenstedt). Section 

 about 2 mm. from the beak, showing relations of apical 

 plate and dental lamellae, x ca. 12. 



the heading "Subgenus Mystrophora" is placed a refer- 

 ence to Quenstedt's figures. At the end of his discus- 

 sion, he names as typical species "M. Lewisii Davids." 

 from the Silurian and "M. areola Quenst." in the 

 order here given. Kozlowski^"' makes the suggestion 

 that if future work on Skenidium and Mystrophora 

 should prove the former to be punctate, the name 

 Skenidium could be used for the punctate species and 

 Mystrophora with "M. lewisii" as the type for the 

 impunctate group. In the absence of definite informa- 

 tion one way or the other, he includes both punctate 

 and impunctate forms under Skenidium. 



It is clear from Kayser's text that he regarded 

 Orthis areola as the type of his subgenus. This view 

 was also held by Williams and Breger,^*"* who say, 

 "The type of Mystrophora was Quenstedt's Orthis 

 areola." Schuchert and LeVene'"* more recently cite 

 Quenstedt's species as the type, and it is so regarded in 

 the present study. 



Williams and Breger evidently considered Mystro- 

 phora a subgenus of Dalmanella in describing D. (M.) 

 elevata. Their species is clearly a dalmanellid, and 

 probably a Wattsella if one can depend on the ventral 

 musculature. 



Mystrophora is an aberrant and specialized dal- 

 manellid paralleling Skenidioides in its internal dorsal 



"^Tal. Polonica, vol. 1, 1929, pp. 46-47. 



"' U. S. Geol. Surv., Prof. Paper 89, 1916, p. 61. 



"* Foss. Cat., Pars 42, 1929, p. 86. 



Structure, but this feature has not yet evolved into the 

 large hinge-plate of Skenidium. 



Genus KAYSERELLA Hall and Clarke 1892 



PI. 16, figs. 7, 8, 10 



Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 259, 

 figs. 15-17. 



Genoholotype. — Orthis lepida Schnur 1853, Pal- 

 aeontogr., vol. 3, p. 218, pi. 45, figs. 9a, b. 



Description. Exterior. — Dalmanelloid, subcircu- 

 lar in outline; hinge-line narrower than the greatest 

 width of the shell; cardinal extremities obtuse; lateral 

 profile unequally biconvex, the ventral valve with the 

 greater convexity; anterior commissure rectimargin- 

 ate; dorsal valve provided with a shallow sulcus. 

 Dorsal interarea long, nearly plane, strongly apsacline, 

 beak very gently curved; delthyrium with elevated 

 margins, partially covered by a convex deltidium; 

 dorsal interarea short, anacline, notothyrium closed by 

 the cardinal process and narrow chilidial plates. Sur- 

 face multicosteUate. Shell punctate. 



Interior. — There was only one specimen of this 

 genus in the Schuchert Collection, and sections of it 

 proved disappointing because the shell is greatly min- 

 eralized. However, a few points regarding the in- 

 ternal structure were obtained. The delthyrial cham- 

 ber is deep and surrounded by adventitious shell, which 

 is also connected with the deltidium. Dental plates 

 were not observed. In the dorsal valve the brachio- 

 phores are long, but the brachiophore plates could not 

 be seen. The cardinal process is lobate as in other 

 dalmanellids. Anterior to the cardinalia the median 

 septum is extended so as nearly to touch the inner wall 

 of the ventral valve, giving exactly the same appearance 

 as in Mystrophora. 



Geologic range. — Middle Devonian of Germany. 



Discussion. — It has been customary for taxonomists 

 to consider Kayserella a streptorhynchid, but, as 

 Kozlowski'"^ has pointed out, the shell is punctate 

 exactly as in Dalmanella. This excludes the genus at 

 once from Streptorhynchus and its allies, since, as this 

 author has also shown, the Strophomenacea all have 

 impunctate shells. Furthermore, the cardinal process 

 is clearly dalmanelloid and not strophomenoid. These 

 two characteristics, then — endopunctate shell and or- 

 thoid cardinal process — are sufficient to place Kayser- 

 ella among the Dalmanellacea. 



The genetic relations of the genus are not yet clear, 

 but as it is best to refer it, on the basis of our present 

 imperfect knowledge, to the family with which it most 

 closely agrees, we place it provisionally with the 

 Mystrophoridae, though it probably does not belong 

 here. We lay least family value on the sporadic reap- 

 pearance of the deltidium and chilidium, and most on 

 the internal features and the dalmanelloid exterior. 



10" Pal. Polonica, vol. 1, 1929, p. 89. 



