26 Marine Shells of the Western Coast of Florida 



The structure of the valves is highly interesting; there are two 

 layers; a quite compact inner stratum and an outer, superficial 

 layer which is perforated by many minute canals perpendicular 

 to the surface, which contain specialized sense organs. In some species 

 these organs have the form of eyes, possessing cornea, lens, pigment 

 layer, and retma. 



Species of three genera belonging to this class are described. 



Order rOLYPLACOPHORA^ 

 Family IS( HNOCHITONIDAE 

 Genus ISCHNOCHITON Gray, 1847 

 Ischnoohiton" pupillosns (C. B. Adams) PI. 1, fig. 1 



Length, 6-8.5; breadth, 5-6 mm. Color mottled olive-green or 

 brown. The sides slope gently and convexly from a moderately keeled 

 mid-ridge. An umbo, central and rounded, on posterior valve. 

 Central and lateral areas of intermediate valves are ill-defined, uni- 

 formly and thickly dotted with minute papillae. The narrow girdle 

 is covered with fine overlapping scales. Interior of the shell white. 



/. papillosus is often found with Chaetopleura apicidata adhering 

 to dead shells of Atrina. 



Genus CHAETOPLEURA Shuttleworth, 1853 

 Chaetoploura' apiculata (Say) PI. 1, fig. 2 



Length, 17-25; breadth, 10-16 mm. Color varies through 

 buflF to ashy-gray or brown, either unicolored or regularly patterned 

 in a darker shade. Occasional specimens are uniformly red or 

 orange color. The dorsum is sharply keeled, the sides slope rather 

 abruptly and are convex. Well-marked oblique lines separate central 

 from lateral areas on each intermediate valve. The central areas 

 bear finely beaded longitudinal riblets. The lateral areas are clearly 

 defined and irregularly dotted with numerous rounded tubercles. 

 The girdle is narrow, with scattered, transparent hairs. Interior 

 white, greenish or grayish. 



Family ACANTHOC HITIDAE 

 Genus ACAIVTHOrHITES (Leach MS.) Risso, 1826 



■'' Gr., polys, many; placs, plate; phcro, carry; shells have eight over-lapping 



plates. 

 8 Gr., isc/ino, slender; chiton, a girdle; Lat., papilla, nipple. 

 ^ Gr., chaitcs, haired; pleura, side; Lat., apiculus, dim. of apex. 



