Vol. IX] BERRY— NOTES ON WEST AMERICAN CHITONS H 



Median valves : lateral areas not in themselves raised, but 

 in front showing a strong, diagonal, rib-like succession of 

 about 10 coarse, somewhat overlapping pustules like those of 

 the primary series on the head valve; on the sutural margin 

 behind a series of large, backwardly directed tubercles like 

 those of the postero-marginal series of the head valve; the 

 flattened area between these two series heavily and closely 

 pustulose with 2-5 variously sized, radial series of granules, 

 with sometimes also one or two similar series in front of the 

 main diagonal rib. Central areas on each side elegantly 

 sculptured with 10-14 sharp, flexuose, longitudinal ribs, 

 curved at first with the concavity inward, but the longer ribs 

 showing a secondary curve in the reverse direction toward 

 the anterior margin; outer ribs more or less broken behind, 

 sometimes resulting in the formation of the aberrant series 

 of granules already noted ; inner face of ribs buttressed by 

 numerous, irregular, claw-like, transverse ridges extending 

 part way across the otherwise merely granular interspaces ; 

 inside ribs more oblique and shorter, in valves iii-vii fusing 

 anteriorly with a single rather weak, median rib along the 

 ridge; valve ii with the jugal rib bifurcating anteriorly, a 

 new median rib developing between the forks, the adjacent 

 ribs of the central areas at the same time more or less 

 anastomosing. 



Posterior valve with the mucro little elevated, strongly 

 posterior in position, the area in front of it sculptured like 

 the central areas of the median valves, but with only 7-8 

 ribs on a side; posterior area coarsely, irregularly, concen- 

 trically rugose, the rugosities best developed in front, where 

 they tend to form a sort of pseudo-rib; slope behind mucro 

 slightly concave. 



Interior of anterior and intermediate valves slightly thick- 

 ened across the middle. Posterior valve with a strong cres- 

 centic callus behind, and a strong, V-shaped, median callus. 

 Teeth short and broad, their bounding fossa at the base 

 shallow but distinct. Sutural laminae of intermediate valves 

 wide, arcuate, in tail valve more angular at margin ; sinus 

 narrow and relatively deep. Insertion slits with rather in- 

 distinct radial lines of transversely slit-like pores leading into 

 them. Eaves short and inconspicuous. Anterior valve with 



