PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 54. 



Family ISCHNOCHITONIDAE. 



Genus ISCHNOCHITON Gray, 1847. 



Subgenus Ischnoradsia Shuttleworth, 1853. 



ISCHNOCHITON (ISCHNORADSIA) ALBRECHTI (Schrenck, 1863). 



Plate 1, figs. 4-5; plate 3, figs. 1-2. 



1863. Chiton Albrechti Schrenck, Bull. Phys.-Math., Acad. Sci. St. Petersburg, 



vol. 5, p. 511. 

 1867. Chiton Albrechti Schrenck, Reisen u. Forsch. Amur-Lande, vol. 2, Zool., 



p. 283, pi. 13, figs. 7-17. 

 1892. Ischnochiton (Ischnoradsia) albrechti Pilsbry, Man. Conch. (1), vol. 14, p. 



147, pi. 19, figs. 70-74. 



Material. — This fine chiton is represented in the collection by two 

 large alcoholic specimens [S. S. B. 83], taken at Mororan, Island of 



Yesso, Japan, July 6, 1906, 

 during one of the shore ex- 

 peditions. One of these is 

 entered as Cat. No. 215627, 

 U.S.N.M. 



Reinarks. — The shell and 

 girdle characters have been 

 well described by Pilsbry, 

 but figures of the radula are 

 now given for the first time 

 (pi. 3, fig. 2). The latter is 

 well developed in this spe- 

 cies, the powerful second 

 laterals being armed with a strong, long, entire cutting edge, and the 

 third laterals having u conspicuous basal process. 



Even in the valves of a single individual great variation appears 

 in the number of insertion plates. The specimen dissected shows 

 the following formula: Anterior valve, 17; intermediate valves, re- 

 spectively, 2-3, 2-2, 1-2, 2-2, 2-3, 2-3; posterior valve, 13 shts. 

 The branchiae number 47-49 on each side, extending practically 

 the entire length of the foot. 



ISCHNOCHITON (ISCHNORADSIA) HAKODADENSIS Carpenter, 1892. 



Plate 1, figs. 6-7; plate 3, figs. 3-5; plate 4, figs. 1-3. 

 1892. Ischnochiton (Ischnoradsia) hakodadensis Pilsbry, ex Carpenter MSS.,Man. 



Conch. (1), vol. 14, p. 147, pi. 19, figs. 64-66. 

 71910. Ischnochiton hakodadensis Thiele, Revis. Syst. Chitonen, vol. 2, pp. Ill, 

 112, pi. 8, fig. 44 (dentition). 



A medium-sized chiton offering several quite puzzhng features was 

 taken rather abundantly by the shore expeditions of the Albatross 

 both at Hakodate, Japan, and at Mororan, a port somewhat farther 

 to the north. The specimens exhibit great variability, not only in 

 color, but in the number of radial riblets (from 5 to 11) and marginal 

 slits, but after much study I am unable to do otherwise than refer the 



VYM^ 



Fig. 1— Ischnochiton albrechti [83], portion of girdle 

 seen from above; camera drawing from a mount in 

 balsam; X 28. 



