106 ISCHNOCHITON. 



Lateral areas slightly raised, sculptured longitudinally with nar- 

 row zigzag groove*, the elevations between them flat, and een under a 

 powerful lens to be most minutely pustulate, the pustules whitish. 

 Central areas covered with an excessively fine, close quincuncial 

 granulation which becomes slightly coarser toward the sides, where the 

 granules gradually become merged into longitudinal rows giving a 

 lirate appearance to the pleura, especially to the part lying at and 

 immediately in front of the diagonal line. End valves having con- 

 centric zigzag grooves and a minute granulation, like the lateral 

 areas ; posterior valve having a moderately elevated, central umbo, 

 posterior slope concave. Interior light gray-blue or white ; anterior 

 valve with 9, central valve 1, posterior valve 9 slits. Teeth smooth, 

 sharp. Eaves narrow, solid ; sutural plates whitish, rather wide 

 and low ; sinus flat, angular. 



Girdle whitish clouded with blue, or blue marbled with white, 

 generally having some small yellow or orange flecks. It is densely 

 covered with imbricating, deeply striated scales. (PI. 20, fig. 24.) 



Length 14 to 15, breadth 8 mill. 



St. Thomas; Barbados. 



Chiton xtriolatus GRAY, Specil. Zool. p. 6 (1828). REEVE, 

 Conch. Icon. t. 22, f. 144. 



The coloring of this species is extremely variable, and the sculpt- 

 ure, while it is unmistakable when seen under a sufficiently high 

 power, still varies considerably. The side areas and end valves 

 are generally sculptured with the concentric zigzag grooves 

 described above (fig. 23) ; but occasionally these become so irregular 

 and broken that the surface appears coarsely granulous or scaly. 

 The West Coast species dispar Sowb. and adamsii Cpr., as 

 well t as the roseus of Sowerby, all belong to the striolatus group, 

 and are closely allied in sculpture. There are also a number of 

 described West Indian Ischnochitons which seem to be either mere 

 synonyms of /. ttriolatn*, or closely allied forms, the exact status 

 of which it is quite impossible to fix with certainty until the origi- 

 nal types can be examined by a competent person, thoroughly 

 acquainted with the subject. The original descriptions of these 

 forms here follow. 



C. *qnamnlo*n* C. B. Adams. Shell olivaceous, ornamented with 

 a pale green dorsal line; lateral areas covered with prostrate 



