ISCHNOCHITON. 65 



Chiton pectinatus SOAVB., Mag. of Nat. Hist., June, 1840, p. 288, 

 t. 10, f. 3; Conch. Illustr. f. 146. REEVE, Conch. Icon. t. 26, f. . 

 133. C. (Ischno chiton) pectinatus SHUTTLEW., Bern. Mittheil. 1853, 

 p. 77. Ischnoplax pectinatus CPR., MS. Chiton acutiliratus 

 REEVE, Conch. Icon. t. 8, f. 46. Chiton multico status C. B.- AD., 

 Proc. Bost. Soc. N. H. ii, p. 8, 1845. 



Readily known from other West India Chitons by its elongated 

 form, speckled and mottled coloring, and especially by the very 

 peculiar girdle. The large scales are distinctly but finely striated. 

 The ground-color of the girdle is pale buff, with patches of olive- 

 green. The large scales are mingled white and buff on the light 

 tracts, and are a dark blue-green on the dark patches. 



Reeve's C. acutiliratus (fig. 30) is a typical pectinatus. I have 

 not seen the Ch. multico status of C. B. Ad., described from Jamaica, 

 and the description is too meager to permit certainty in referring it 

 here. 



Subgenus IV. HETEROZONA Carpenter, 1878. 



Heterozona CPR. (Table of Regular Chitons, 1873), DALL, Proc. 

 U. S. Nat. Mus. 1878, p. 331. Type H. cariosa Cpr. MS. 



Shell like normal Ischnochiton ; girdle bearing small scales with 

 large striated scales intermingled. 



The girdle is that of Ischnoplax, but the shell is not elongated, 

 and the umbo of the posterior valve is median, not posterior. The 

 arrangement of scales normal in this section is the same as a patho- 

 logic condition sometimes met with in individuals of species 

 normally having regular and equal scales, but in which the girdle 

 has been injured; the injury being repaired with scales much 

 smaller than those upon the healthy portions of the girdle. 



I. CARIOSUS Carpenter, n. sp. PI. 24, figs. 20, 21, 22. 



Shell oblong, rather elevated, the valves broadly arched and 

 rounded dorsally. Color, soiled yellowish, unicolored or with 

 indistinct brown spots. 



The lateral areas are raised, and sculptured with a varying num- 

 ber (about 7) of radial ribs, which are irregular, often splitting, 

 and very unevenly granose. Central areas finely granulated upon 

 the dorsal ridge, the granulation giving place on the side-slopes to 

 a rather strong but fine corrugation ; the wrinkles longitudinal, 

 but converging forward toward the middle; and minutely irregular 



