PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 331 



4. Hetcrozona Cpr H. cariosa Cpr. 



Body elongate ; two kinds of rather solid, striated scales. 



5. Ischnochiton (restricted) Cpr C. longicymba Quoy. 



Scales transverse, flattened, somewhat imbricated, generally striated. 



6. Isclmoradsia Cpr. ex Shuttle worth , C. dispar Sowerby. 



Scales striated. Central valves with many slits. 



7. Lepidopleurus Cpr Ex C. Mcrtcnm Midd. 



Scales solid, imbricated, smooth. 



8. Lepidoradsia Cpr C. australis Sowerby. 



Similar to the last, with many slits in central valves. 



The only Alaskan species of the restricted subgenus, so far as known, 

 is the following form. 



Ischnochiton interstinctus. 



Chiton interstinctus Gould, Moll. U. S. Expl. Exp. p. 322, pL 27, f. 423, a, h, 1?52. 

 C. {Leptochiton) interstinctus Gould, Otia, p. 230, 242, 1862. 

 Callochiton interstinctus H. & A. Adams, Gen. Rec. Moll, i, p. 471, 1654. 

 Trachydermon interstinctus Cpr. Suppl. Rep. Br. As. 1863, p. 649. 

 Ischnochiton interstinctus Cpr. MS. 1871. 



1. 1. mucrone antice mecliano, satis elevato; intus v. post. 12-, ant. 10-, 

 centr. 1-fiss. ; dent, acutis ; subgrundis modicis ; sinu lato, planato ; zona 

 squamulis subovalibus, tenuissinie striatis. Lon. 17, Lat. 7 mm. Div. 

 110° 



Rab. — Sitka Harbor, 12 fathoms, mud and gravel! south to Monterey 

 and the Santa Barbara Islands, California. Eighty-seven specimens 

 examined. 



This is a modest little species of a dark red color, mottled with light 

 about the jugum. The riblets are somewhat broken into tubercles by 

 the lines of growth. It appeared to be very abundant at Sitka in the 

 locality where it was found. There are no other species likely to be con- 

 founded with it in this district. 



The gill-rows are nearly as long as the foot. The muzzle is produced 

 into lappets at the corners. Xo data in regard to the fenestra? could be 

 obtained from the dry specimens. 



Ischnoradsia trifida. 



Trachydermon trifidus Cpr. Suppl. Rep. Br. As. 1863, p. 649; Proc. Phil. Acad. 

 Nat Sci. 18C5, p. 60. 



I. satis magna, satis elevata, regulariter ovali ; rufo-castanea, pallidiore 

 et intensiore maculata; jugo acutiore, gothico; mucrone mediano, pla- 

 nato; tota superficie vix minutissime granulata; ar. centrali lineis trans- 

 versis, jugo perpendicularibus circ. VIII altissime punctatis; ar. lat. 

 valde definitis, costis obsoletis II-IV, interdum ad interstitiis punctim- 

 depressis; intus, pagiua interna albido-carnea, radiis II rufo-purpureis 

 ab umbonibus planatis divergentibus; v. post. 33-, v. ant. 13-, centr. 2- 

 fissatis, dentibus acutis interdum ad inargines serratis, interdum extus 

 striatis sed interdum normaliter Uevibus; subgrondis Qonspicuis sub- 



