1011.] NATURAL SCIENCES OF PHILADELPHIA. 487 



A NEW CALIFORNIAN CHITON. 



BY S. S. BERRY. 



Through the kindness of Dr. Harold Heath, of Stanford Uni- 

 versity, I have had placed at my disposal a series of small chitons 

 dredged by him in Monterey Bay, Cal. Among them are several 

 specimens of the curious Mopalia heathii and an equally aberrant 

 allied species which seems undescribed. To contain these anomalous 

 forms, I propose the following new group. 



DENDKOCHITON nov. subgenus. 



Species small; valves divided into more or less distinct areas in 

 the usual manner; insertion plates as in Ischnochiton, the posterior 

 valve without a posterior-median sinus. Valve I with 7-8 slits; 

 valves II-VII with 1,1 slits; valve VIII with 6-8 slits. Sculpture 

 variable, as in Mopalia. Girdle covered above with minute ovoid 

 spinelets or spicules, larger on the lower surface. Sutural and 

 intersutural tufts present, the former well developed with a very 

 long and branching central bristle. 



This subgenus in large measure breaks up the distinction between 

 the Mopaliidw and the Ischnochitonidce, presenting many of the 

 features proper to both groups. In this connection it should be 

 remarked that the girdle of even the true Mopalias is not strictly 

 nude, but in the young, at least, is furnished (though not densely) 

 with minute spinelets very similar to those of Dendrochiton. 



Type: the following species. 



Mopalia (Dendrochiton) tnamnopora n. *p. Plate XL, figs. 4, 5, 6, 8. 



Shell small, oblong, rather narrow for Mopalia, much elevated 

 and strongly carinated, the side slopes nearly straight. 



Valves sharply beaked in front; the lateral areas fairly well 

 defined, not raised, having a few very faint radial grooves, but 

 without well-marked sutural or diagonal ribs. Central areas orna- 

 mented with a series of about nine or ten very strong, low, broad, 

 longitudinal riblets, curved and converging toward the median 

 ridge; their intervals of nearly equal breadth, not latticed or other- 

 wise sculptured. On the jugal tract these ribs are obsolete or 

 wanting. Entire surface minutely granular-porous, but not so 



