22 PROCEEDINGS OF THE NATIONAL MUSEUM vol.80 



later authors have deviated from the type of the species until the 

 later determinations show little relationship to the original. For 

 this reason, in many cases, only the first reference is given in the 

 synonymy. 



ROBULUS WILLIAMSONI (Reuss) 



Plate 6, Fiqtjees 7 a, & 



Cristellaria vnlUamsoni Reuss, Sitz. Akad. Wiss. Wien, vol. 44, pt. 6, p. 327, pi. 

 6, figs. 4 0, 6, 1861 (1862). — Cushman and Church, Proc. California Acad. 

 Sci., ser. 4, vol. 18, no. 16, p. 503, pi. 36, figs. 13, 14, 1929. 



The specimen figured here is very close to the typical form figured 

 and described by Reuss from the Cretaceous of Germany. It has a 

 distinct keel, few chambers, depressed and slightly curved sutures, 

 and a smooth surface. The apertural face is distinctly concave with 

 raised edges. 



ROBULUS OLIGOSTEGIA (Reass) 



Plate 6, Figukes 8, 9 



Cristellaria oligostegia Reuss, Sitz. Akad. Wiss. Wien, vol. 40, p. 213, pi. 8, 

 fig. 8, 1860; vol. 46, pt. 1, p. 93, pi. 13, figs. 2 a, i, 1862 (1863). 



This is a very thick species with a few tumid chambers, the later 

 ones showing a slight tendency to uncoil. The aperture is slightly 

 protuberant. 



ROBULUS STERNALIS (Berthelin) 



Plate 6, Figukes 11 a, b 



Cristellaria sternalis Berthelin, Mem. Soc. G§ol. France, s6r. 3, vol. 1, p. 51, 

 pi. 3 (26), figs. 2 a, b, 1880. 



This species may be distinguished from R. wilUamsoni by the dis- 

 tinctly umbonate character of the test. The angle of the sutures is 

 very different in the two species, as are also the shape and form of the 

 chambers. 



ROBULUS TRINITATENSIS. new species 

 Plate 6, Figures 10 a, h 



Description. — Test close coiled, compressed, periphery slightly 

 keeled ; chambers fairly distinct, 6 to 8 in number in the adult, not 

 inflated ; sutures fairly distinct, strongly curved, continuing into the 

 umbilical region, strongly limbate, but not raised ; wall ornamented 

 by a series of obliquely curved costae, toward the periphery grad- 

 ually becoming nearly parallel to the outer edge of the test, and con- 

 tinuous over the chambers; aperture at the peripheral angle, with a 

 supplementary elongate opening in the median line of the ventral 

 face. Length, 0.5; breadth, 0.4; diameter, 0.2 mm. 



