588 CAMBRIAN BRACHIOPODA. 



valves (PI. LIV, figs, le, 2g, 2h), also in the same valves it passes closely around the muscle 

 scars situated between the main siauses and reaches the base of the area in line with the 

 flexure line of the area; in the dorsal vah^e it closely follows the outside limits of the muscle 

 scars, but it has not been traced across the main vascular sinuses. 



The size and position of the pedicle and umbonal muscle scars is unknown, but they are 

 probably similar to those of Oholus. The central scars (h) (PI. LIV, figs. Ih, 2k, 2 1) are placed 

 a little distance each side of the median line in the dorsal valve; in the vential valve they are 

 not separable from the middle and outside laterals, which occur on each side of the front of 

 the visceral area at (c) (PI. LIV, fig. 2h). The middle and outside laterals of the dorsal valve 

 (1) are blended and lie obliquely outward before the transmedian scars (i). The transmedian 

 scars are close to the base of the area in both valves, and lie in the line of the prolongation of 

 the flexure line of the area. In number and relative position the muscle scars of OboleUa as 

 far as known are essentially the same as in Oholus. 



Ohservations. — The genus OboleUa has been under discussion by authors for over fifty 

 years. In the original description Billings [1861b, p. 7] noted its resemblance to Oholus but 

 claimed that it was distinct on account of the difference in "the arrangement of the muscular 

 impressions." Later [1872c, p. 356] he compared it again mth Oholus, but having poor illus- 

 trations of both Oholus and Oholella he failed to discover the true position and relations of the 

 muscle scars in either. It was not until after Mickwitz's memoir [1896] on Oholus appeared, 

 and the collections of Oholella made under my direction during the summer of 1899 were studied, 

 that any correct comparisons could be made. It then became evident that as far as known 

 there was practically no difference in the arrangement of the muscle scars of the two genera, 

 but that there were most essential differences in the cardinal area of the ventral valve. Before 

 working out the fact that the ventral valve was perforated by a pedicle tube or foramen, I was 

 at a loss to find generic difference of value, although I believed that the area of the dorsal 

 valve of Oholella indicated differences not readily explained. 



The pedicle passage of Oholus varies greatly in size and form, but it is always an open 

 furrow. In Oholella, it is in the ventral valve a cylmdroconical tube, the cardinal area rising 

 from the plane of the margin of the valve beneath the pedicle tube; in the dorsal valve a 

 slightly raised area occupies the place of the broad furrow in Oholus. 



Oholella is confined to the Olenellus or Lower Cambrian fauna. Oholus, as now limited, 

 appears in the Lower Cambrian, and has its greatest development in the Middle and Upper 

 Cambrian fauna. 



Bicia gemma is associated with Oholella crassa both at Bic and Troy, and the species was 

 referred to Oholella by Billings [lS72a, p. 218]. It differs so radically from Oholella in the 

 character of the areas of the valves and the interior markings that it is scarcely necessary to 

 institute comparisons between them. Lingulella schucherti is found associated with Oholella 

 crassa at Troy, New York. 



The interior markings of Oholella and Botsfordia are quite similar (Pis. LiV and LV, and 

 Pis. LVII and LIX). The same is true of Trematoholus (PI. LXXXIII), but the pedicle open- 

 ing of Botsfordia is above the beak with almost no area beneath, while that of Oholella is above 

 a well-defined false area, and that of Trematoholus is more in advance of the beak. 



Obolella asiatica Walcott. 



V 



Plate LV, figures 6, 6a. 



Obolella asiatica Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 297. (Described and discussed as below as a new 

 species.) 



General form broad, ovai, with the ventral valve showing a tendency to become bluntly 

 acuminate. Valves gently convex. Surface of shell marked by concentric, raised lines of 

 growth that form the front edge of narrow lamelhe of varying width; the raised lines are highest 

 in front, which gives an imbricated appearance to the surface; fuie concentric striae occur on 

 the interspaces between the raised Imes. Shell strong, apparently calcareous. 



