144 ISCHNOCHITON-ISCHNORADSIA. 



be expected to occur in any branch of Chitons; from the genus 

 Ischnochiton alone, we have at least four or five independent 

 Radsioid branches. 



The typical J. tiyrinus of Krauss is striped longitudinally. The 

 unstriped form, of which several specimens are before me, may be 

 called var. unicolor. 



The species mentioned by Carpenter as I. subcariosa may be a 

 form of I. tigrinus. The type is a single specimen of unknown 

 origin, and is in the museum of McGill College, Montreal. 



Subgenus VII. ISCHNORADSIA Shuttleworth, 1853. 



Ischnoradsia SHUTTLW., Berner Mittheil. 1853, p. 65, species cited 

 C. australis and C. magdalenensis. Not Ischnoradsia CPR. Lepido- 

 radsia CARPENTER, MS. ; and DALL, Proc. U. S. Nat. Mus. 1878, 

 p. 331, type C. australis. 



Valves having sharp but rather thick insertion plates, those of 

 the median valves with two or several slits. Girdle covered with 

 convex, pebble-like, smooth scales. Type Chiton australis Sowb. 



The typical forms of this section are from the Australian seas, but- 

 several species have also been found in Japanese waters. 



Carpenter's substitution of the name ' Lepidoradsia ' in place of 

 Ischnoradsia, was in direct violation of the rules of nomenclature. 



Key to species. 



a. Sinus dentate within, albrechti* 



aa. Sinus smooth. 



b. Central areas longitudinally ribbed, australis, luyubris. 

 bb. Central areas minutely granulated. 



c. Outside green, inside green and pink ; scales very convex, 



novcehollandice. 

 cc. No green or pink ; scales small, convex, hakodadensis. 



I. AUSTRALIS Sowerby. PI. 18, figs. 57, 58, 59. 



Shell oval-oblong, moderately elevated, the dorsal ridge sub- 

 angular, side-slopes nearly straight. Color dark olive-brown, the 

 apices of the valves pink when eroded. 



Lateral areas somewhat raised and sculptured with close, uneven 

 riblets, which usually bifurcate or branch freely, especially toward 

 the posterior margin of the area. Central areas closely and evenly 



