133 Bulletin 13 21 



His argument for Pelecypod relationship is based on the 

 presence ot" a small aperture of semi-circular shape "just beneath 

 the umbo and in front of it which appears to be the entrance to a 

 tubular passage running br.ckwards over the transverse plate into 

 the general cavity of the body." This cavity he supposed "served 

 the function of a byssal orifice and that these species were anch- 

 ored by a byssus passing through the beak." He placed his 

 species in the genus Ribeina provisionally and proposed the name 

 Ribeirina if further examination showed a .separation necessary. 



After a full discussion of the genus. Whitfield (A. M. N. H., 

 vol. r, p. 343, 1 88 1 -86) says: "I think there can be no question 

 about their relationship to the Ceratiocaridae (or Phyllocaridse, if 

 we adopt Prof. Packard's new name)." 



In Eastman's translation of Zittel's Text Book of Paleontol- 

 ogy, 1899, is this statement: "There is no satisfactory evidence 

 of their Crustacean nature." 



Our species belongs to that division of the genus to which 

 R. calif er Bill., R. longiuscida Bill, and R. comprcssa Whit, are 

 referred. Without going into a further discussion of the relation- 

 ships, it should be said, however, that there is .so much doubt as 

 to the corredlness of the identification with Sharpe's genus that 

 we refer our species to it with a great deal of doubt. 



Ribeiria (?) nucuiitiformis, n. s., PI. 16, figs. 10, 11, 12, 13, 14 



vShell small, resembling, in general appearance, a nuculite. 

 Compressed laterally; about one-half as high as long. Dorsal 

 margin concave, sides convex. In the casts of the shell the an- 

 terior is rounded, with a deep notch just below the beak. Notch 

 about one-quarter as long as the shell, extending obliquely toward 

 the middle of the ventral .side. The shell is not bilaterally sym- 

 metr ical. From PI. 16, fig. 12, it will be seen that there is a 

 sinus and fold on the right side and a corresponding fold and 

 sinus on the left. 



Surface smooth as far as known. 



This species resembles R. calcifer Bill., but differs in the 

 presence of the fold near the dorsum and in the depth of the 

 notch. 



Size varies from r '2 mm. wide by 3 nnn. long to 6 b>- 1 2 nun. 



An extremely abundant fossil in bed \T 3 and occasionally 

 found in \' 2 of the Ft. Hunter section. 



