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VOL. 83 



of the shell at the center, the highest point, is about 105 mm, prob- 

 ably more in life, since there is some indication of vertical com- 

 pression. 



The very rough surface ornamentation of the carapace (see 

 pi. 14) is quite characteristic of this species, and this feature alone 

 is sufficient to distinguish it from all described baenids with the 

 possible exception of Baena nodosa Gilmore, which also occurs in 

 this same formation. 



The ornamentation consists of a series of elongate, longitudinal, 

 round-topped ridges and low, rounded, nodelike protuberances. 



These are arranged 

 in alternate t r a n s- 

 verse bands across 

 the mid region of 

 the shell, extending 

 somewhat outside of 

 the vertebral areas, 

 where they are 

 sparser and less reg- 

 ular in their place- 

 ment. In the type 

 there is a median 

 ridge formed by 

 t h r e e and four of 

 these elongated ele- 

 vations set closely 

 parallel with narrow 

 grooves between. 

 This ridge is not con- 

 tinuous but i n t e r- 

 rupted a t intervals 

 where the transverse 

 bands of rounded 

 nodes cross from one side to the other. In U.S.N.M, no. 12821, which 

 clearly pertains to this species, this ridge is made by a single elevation, 

 although the other sculpture is quite similar to that of the type speci- 

 men. The outer half of the costal area and the whole posterior fourth 

 of the shell have an undulating surface, but plain except for a few low 

 scattered nodes. The surface is not smooth but slightly wrinkled, 

 wnth a shagreened appearance resulting. The peripheral surfaces 

 are fairly smooth, except along the front of the shell, where they are 

 ornamented by low, irregularly shaped elevations. 



Figure 7. — Carapace of Bacna ornata, new species. 

 Type. U.S.N.M. no. 13229. VI, V5, Vertebrals 1 and 

 5, respectively. One-sixth natural size. 



