GENERA OF THE SUBORDER ORTHOIDEA 



125 



The genetic relations of the Wattscllida: appear to 

 be as shown in Table 1 0. 



Genus WATTSELLA Bancroft 1928 



PI. 22, figs. 9, 13, 14, 17-29 



Bancroft, Mem. Proc. M.inchester Lit. and Philos. Soc., 

 vol. 72, 1928, p. 55, pi. 1, figs. 1-5. 



Genoholotype. — Watisella wattsi Bancroft 1 928. 



Description. Exterior. — Subcircular, hinge-line 

 straight, narrower than the greatest width of the shell; 

 cardinal extremities rounded; lateral profile unequally 

 biconvex, the ventral valve .ilways with the greater 



Table 10 



Fascicostella 



Parmorthis 



Idiorthis <■ 



Mendacella 



> Horderleyella 



Resserella 



Dalmanellio^ 



convexity. Anterior commissure rectimarginate to 

 faintly sulcate. Dorsal sulcus shallow, deepest posteri- 

 orly; ventral fold conspicuous only at the posterior. 

 Ventral palintrope longer than the dorsal, curved, apsa- 

 cline, beak incurved, umbo strongly convex. Dorsal 

 palintrope short, faintly anacline, beak inconspicuous; 

 umbo sulcate, delthyrium and notothyrium open. Sur- 

 face multicostellate ; shell fibrous, punctate. 



Ventral interior. — Delthyrial cavity deep; teeth 

 strong; crural fossettes deep; dental plates sharp, 

 divergent, commonly continued forward as a ridge on 

 the lateral periphery of the diductor scars. Muscle 

 area subcordate, more or less gently bilobed in front. 

 Adductor track linear, squarish in front. Diductor 

 scars elongate, rounded in front, and narrowing 

 behind; adjustor scars not separable. 



Dorsal interior. — Cardinalia prominent, brachio- 

 phores elongated into slender points, extending nearly 

 directly ventrally; brachiophore supports triangular in 

 side view, convergent, and uniting with the median 

 ridge; sockets defined by a small fulcral plate. Car- 



dinal process small; shaft slender, and only defined 

 in the sp.icc between the brachiophore supports; myo- 

 phorc lobed. Median ridge prominent, extending to 

 the middle of the valve; muscle area oval, widest in 

 front. Anterior adductor scars the larger. 



Geologic range. — Upper Ordovician into early 

 Silurian. 



American Species 



Dalmdnella edgezvooJensis Savage 1913 

 Shells of this genus are common in eastern North America 

 and are now parading as Dalmanella tesludinaria 



European Species 



Orthis tesludinaria Dalman 1828 

 Terebratula miguis Sowerby 1839 

 Watisella wattsi Bancroft 1928 



? W. multiflicata Bancroft 1928 



Distinguishing characters. — This genus differs 

 from Dalmanella in its more cordate muscle area, the 

 subparallel brachiophore supports which converge dor- 

 sally to meet the median ridge, the presence of fulcral 

 plates defining the socket, and the exceedingly long 

 tenuous brachiophores. 



Discussion. — In restricting Dalmanella to shells of 

 the type of Orthis rogata Sardeson, which Hall and 

 Clarke mistakenly identified as Orthis testudinarta 

 Dalman, the writers have left the European dalman- 

 ellid group without a proper generic name. Bancroft's 

 recently proposed Wattsella has a structure identical 

 with that of Orthis testudinarta Dalman and must 

 therefore include that species. Bancroft laid generic 

 value on the differences in the cardinalia of the dal- 

 manellids and based several genera on their variations. 



The cardinalia of Wattsella, as well as the ventral 

 musculature, are strikingly different from those of 

 Dalmanella as restricted by us. In the latter genus 

 the diverging brachiophores are typically bladelike, and 

 are never provided with fulcral plates defining the 

 socket. In Wattsella, on the other hand, the brachio- 

 phore plates converge dorsally to meet the outside 

 margins of the median ridge. It is these plates that 

 make the parallel slots in internal molds (see pi. 22, 

 fig. 20). The median ridge extends to the middle of 

 the valve, is low and wide. The cardinal process is 

 normally rather small, with a short shaft and trilobcd 

 myophore which in its lateral lobes in adults or old 

 forms may be extended anteriorly some distance. 

 When such is the case, it gives this structure the appear- 

 ance of being fissured. In some specimens the median 

 lobe may be extended forward along the shaft as in 

 Isorthis, so that the cardinal process simulates in form 

 the head of a bee or fly. 



In mature forms of Wattsella, as in most other 

 genera of the Dalmanellacea, adventitious shell is 

 deposited about the brachiophore plates. In the genus 



