Boone, Mollusca, Cruises of "Eagle" and "Ara," 1921-28 199 



GASTEROPODA. 



AMPHINEURA. 



Subclass: Isopleura. 



Order: POLYPLACOPHORA. 



Superfamily : Mesoplacophora. 



Family: ISCHNOCHITONIDAE. 



Genus: ISCHNOCHITON Gray. 



Subgenus : Stenoplax Carpenter, s.s. 



Ischnochiton (Stenoplax) limaciformis Sowerby. 



Plate 125, fig. A. 



Type: The type material was collected at Lobos Island, Peru, and 

 Guaycomayo, Central America, by Hugh Cuming. Depository not 

 stated. 



Distribution: Mazatlan, Mexico, southward to the Lobos Islands, 

 Peru, and also in the West Indies. According to Dr. Dall, it is, per- 

 haps, also found in Japan. 



Material examined : One specimen, dredged in 5 fms., American 

 Shoal Light, Florida, by the "Ara." This is a very large specimen. 



Color: Dorsally buff-gray or greenish, indistinctly mottled with 

 darker tones and sometimes spotted with red ; ventral surface stained 

 with bright pink and blue-green. 



Technical description : Shell very elongated, narrow, elevated, well 

 arched, costulate longitudinally. 



Anterior valve: Finely sculptured with close, regular, concentric 

 ridge, composed or irregular, wavy lines, also marked by occasional 

 lines, indicating arrested growth development. Eleven slits are 

 present. 



Intermediate valves : The central areas are separated from the lat- 

 eral areas by a decided obtuse ridge, the lateral areas being well ele- 

 vated. The sculpture on the central areas consists of fine longitudinal 

 riblets, separated by interstices of equivalent width ; these riblets are 

 continued upon the lateral areas, becoming heavier and wider there 

 and being distinctly wavier on the slope between the two areas. One 

 slit is present in each valve. 



Posterior valve: With the umbo subcentral, not very high; the 

 central region marked with fine longitudinal riblets as on the other 

 valves, and with the posterolateral slope behind the umbo sculptured 

 with concentric rings of wavy ridges. Nine slits are present. 



