Vol. XI] BERRY— FOSSIL CHITONS 479 



Description: Head valve moderate in height, crescentic, 

 ornamented above by about 32-47 strong, rounded or slightly 

 flattened, radiating ribs, more numerous toward the margin. 

 occasionally bifurcating, but for the most part simple and 

 slightly wider than their finely, distinctly, closely granulated 

 interspaces. Posterior margins further decorated by a series 

 of about 10 short, strong, crescentic ridges, lying somewhat 

 obliquely transverse of the radii. Interior with a low, irregu- 

 lar, transverse callus. Slits 11, each connected with the apex 

 of the valve by a conspicuous series of transverse, slit-like 

 pores. Teeth sharp, strongly beveled, scarcely longer than the 

 solid, somewhat overhanging, crenulated eaves. 



'Median valves comparatively short and wide, strongly ele- 

 vated, with a fairly sharp dorsal ridge and comparatively- 

 straight side slopes; not beaked. Lateral areas sharply de- 

 fined, moderately elevated, sculptured much as above described 

 for the head valve, the 4-5 radial ribs separated by rather nar- 

 rower granular interspaces, and the posterior margin rendered 

 weakly dentate by a series of perhaps a dozen crescentic tuber- 

 cles placed obliquely transversely to the marginal radius. Jugal 

 tract not well defined. Entire central area sculptured by 

 numerous (in largest specimens about 25-28 on a side), fine, 

 usually nearly straight, often nodulose, longitudinal riblets, ap- 

 pearing not quite so wide as their abrupt, deeply cut inter- 

 spaces, and connected across the latter by rather coarse con- 

 centric threadings corresponding in their course somewhat to 

 the lines of growth and on a lower level than the longitudinal 

 riblets. Jugal region with the longitudinal bars still parallel, 

 but with the transverse sculpture weaker than on the slopes. 

 Interior with a strong, transverse, obtusely V-shaped callus. 

 Sutural lamina? evenly arcuate, short and broad, connected 

 across the shallow sinus by a short, toothed plate, which, when 

 perfect, may project past the tegmentum; 5-6 more or less 

 irregular, sometimes ill-defined, series of transverse, slit-like 

 pores apparently corresponding in position to the slits in this 

 plate. Insertion teeth scarcely beveled and more projecting 

 than those of the head valve. Slits 1-1. a conspicuous radial 

 series of the transverse, slit-like pores running to their apices. 

 Eaves overhanging. 



Tail valve with low, subcentral mucro. Posterior area ele- 

 vated toward the sides in front, slightly concave behind the 



