ISCHNOCHITON. 61 



Section Stenoradsia Carpenter, 1878. 



Stenoradsia CPR. (MS., and table of Reg. Chitons, 1873), BALL, 

 Proc. U. S. Nat. Mus. 1878, p. 330, type C. magdalenensis Hinds. 

 Maugerella CPR. MS. and table of Reg. Chitons, type M. conspicua 

 Cpr. MS. Ischnoradsia (in part), SHUTTLEW., Bern. Mittheil. 1853, 

 p. 66. 



Like Stenoplax, but intermediate valves having several side slits. 



The Radsioid valves alone distinguish this from Stenoplax. Its 

 relations with the Australian Stenochiton juloides are probably not 

 especially close. 



In one species, /. conspicuus, the mantle scales have been trans- 

 formed into short, round, striated bristles, and on account of this 

 modification Carpenter established for it a subgenus under C/iceto- 

 pleura which he called Maugerella. We are compelled to suppress this 

 group because of the excessively close relationship existing between 

 I. conspicuus and the two species of genuine Stenoradsia, I. acrior 

 and I. magdalenensis. 



I. ACRIOR Carpenter, n. sp. PL 14, figs. 86-89. 



Shell much like I. magdalenensis, but broader and flatter, with 

 much sharper sculpture. Olive-green, pink where worn, or some- 

 times light flesh-colored, with the jugum or central areas often 

 green. Girdle dark ashen or olive. 



The anterior valve is notably concave, as in I. conspicuus. The 

 lateral areas are much raised, and sculptured with acute radiating 

 riblets, sometimes splitting; central areas having acute longitudinal 

 riblets. 



Interior pink, with a blue spot at the jugal sinus. Sutural plates 

 wide, pink ; sinus broad, deep, angular. Anterior valves having 

 13-15, central valves 2-4, posterior valves 10-13 slits. Teeth long, 

 sharp, smooth. Eaves wide, dark-blue. 



Girdle wide, tough, covered with very small, solid, short scales. 



Length 110, breadth 55 mill. 



Length 75, breadth 40 mill. 



Cerros (Cedros) Island to Cape St. Lucas, Lower California. 



Stenoradsia acrior CPR. MS. Chiton magdalenensis (part) REEVE, 

 Conch. Icon. t. 4, f. 20a, not of Hinds. 



This species represents one extreme of variation of the 1. 

 magdalenensis type, the other extreme being 1. conspicuus. I have 



