PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 331 



4. Hetcrozona Cpr H. cariosa Cpr. 



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



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



Scales transverse, flattened, somewliat imbricated, generally striated. 



6. Isclmoradsia Cpr. ex Shuttlewortli , C. dispar Sowerby. 



Scales striated. Central valves with many slits. 



7. Lepidopleurus Cpr ■. Ex C. JicrfcHsi Midd. 



Scales solid, imbricated, smooth. 



8. Lepldoradsia Cpr ,C austraVis Sowerby. 



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



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

 is the following form. 



Ischnochiton interstinctus. 



CUton interstinctus Gould, Moll. U. S. Expl. Exp. p. 322, pi. 27, f. 423, a, 1, 1852. 

 C. (Leptochiton) interstinctws Gould, Otia, p. 230, 242, 1862. 

 Callochiton interstinctus H. & A. Adams, Gen. Rec. Moll, i, p. 471, 1854. 

 Trachydermon interstinctus Cpr. Suppl. Eep. Br. As. 1863, -p. 649. 

 Ischnochiton interstinctus Cpr. MS. 1871. 



I. t. mucrone antice inediano, satis elevato; intvs v. post. 12-, ant. 10-, 



centr. 1-fiss. ; dent, acutis ; subgrundis modieis ; sinu lato, plauato; some 



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



llOo. 



Hah. — 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 b}' 

 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 giU-rows are nearly as long as the foot. The muzzle is X)roduced 

 into lappets at the corners. Ko data in regard to the fenestras could be 

 obtained from the dry specimens. 



Ischnoradijia trifida. 



Trachydermon trifidus Cpr. Suppl. Eep. Br. As. 1853, p. 649; Proc. Phil. Acad. 

 Nat Sci. 1865, p. 60. 



I. satis magna, satis elevata, regnlariterovali; rufo-castanea, pallidiore 

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

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

 versis, jugo perpendicularibus circ. YIII altissime puuctatis; ar. lat. 

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

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

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

 fissatis, dentibus acutis interdum ad margines serratis, interdum extus 

 striatis sed interdum normalitcr laivibus; subgrundis consi)icuis sub- 



