iwiLLiAMs] FOSSIL FAUNAS OF THE ST. HELEN'S BRECCIAS 231 



17a. A small specimen of a pedicle valve presenting the typical 

 form of " Strophomena woolwortliana/' i.e. " ventral valve concave 

 towards the front and flat on the lateral margin, depressed convex near 

 the beak '' might be referred to that species, but it is more probable that 

 it is only a variation of the form I have Hated above under the species 

 Orthothetes deformis, Hall. 



18. Gypidula pseudoyaleala. Hall. 



Several rather small sized specimens, the largest about 20 mm. 

 total length, present the ordinary characters of this species of the 

 Helderberg fauna of New York. 



19. Rhynchonella cf. planoconvexa. Hall. 



A single dorsal valve ha\àng the broad regularly arched form of 

 tlie species R. planiconvexa. Hall, has one of the plications bifurcating. 

 The number of plicationis on the body of the shell is only 18, but the 

 front of the specimen is broken. There is a very indistinct flattened 

 fold rising slightly above the general surface. The specimen is referred 

 to this species. The plications are larger than upon R. vellicatus which 

 has teimilar form. 



20. Camarotœcliia veniricosa, Hall. 



This characteristic Helderbergian species is represented by numer- 

 ous specimens of ordinary size and often is extremely gibbous. 



21. Rhynchotrema formosum, Hall. 



This species is also represented by numerous specimens showing the 

 variability expressed by the species in tlie Helderberg limestone of New 

 York State. 



22. Spirifer concinnus, Hall. 



Numerous specimens of typical S. concinnus are represented in the 

 fauna. They are of smaller average size than the typical species of the 

 Lower Helderberg of New York and the interior, but otherwise exhibit 

 the ordinary characters of that species ; none of them show the rudi- 

 mentary plications of fold and sinus ascribed to a variety of the species. 



23. Spirifer concinnus var. Helenœ n. var. 



One gibbous specimen presents varietal characters wliich may be 

 signified by the name Spirifer concinnus var. Helenœ. It appears to be 

 full grown, the general form is more gibbous than normal, and the 

 cardinal extremities are well rounded. The outline is approximately 

 that shown by the specimens figured by Hall aç 8. cyclopterus, marked 

 In on Plate 25,i but it differs from the species 8. cyclopterus by the 

 greater number (11 and 12 each side the sinus) and smaller size of the 

 plications, showing in this respect the characteristics of C. concinnus. Its 

 dimensions are, width 28.5 mm., height 25.4, thickness of the two valves 



1 Pal. N. Y., Vol. Ill, Plate 25, Fig. In. 



Sec. IV., 1909. 14. 



