from the Vancouver District. 425 



moored hy byssus, like Modiola. The largest known species is 

 A.falcata, Gld., which is normally straight, but often grows in 

 a twisted burrow. A. parasitica] Desh., and the long-known 

 A. cinnamomea appear congeneric, 



13. Adida stylina. 



A. testa cylindracea, lithophagoidea, leevi, tenuissima, parum ar- 

 cuata, subnacrca, albida, postice interdum Undo tincta ; epider- 

 iiiide nitente, Isevi, solidicre, nigro-fusca : testa jun. typice medio- 

 la.*formi, umbonibus subanticis, obtusissimis ; margine dorsali 

 antice (rarissime paululum, testa minima, postice) teniiiter crenu- 

 lato : testa adulta marginibus dors, et ventr. fere parallelis, ant. 

 ct post, rotundatis ; umbonibus detritis, hand conspicuis, circiter 

 sextantim antice sitis ; incrustatione baud soiida, densissime spon- 

 giosa, aream posticam diagonalem tegente, supra valvas prolongata, 

 appressa ; ligamento intemo, postice valde prolongate ; pagina 

 interna pallida ; cicatr. add. postica tumida, pyriformi, antica 

 (quoad familiam) maxima, hand iraprcssa, oblonga ; cicatr. pedali 

 aiitica magna, circular!, impressa ; callositate subumbonali (testa 

 jun.) cicatr. pcdalem versus conspicua. Long, 'loo, lat. '4, alt. "5. 



Variat t. magis arcuata; ut in A. falcata, autice tumidiore, sub- 

 angulata. 



Variat quoque testa attenuata. 



Yariat interdum ventraliter late lilante. 



Hab, Necah Bay, abundant {Swan) ; Monterey {Taylor). 



On smashing a large lump of hard clay, bored by Pholads, 

 Petricolids, &c., large numbers of this species, with a few of A, 

 falcata, of all ages from '00 onwards, were found in situ. Several 

 struggled for room in a single cr)pt. The umbos are abraded 

 by the wide opening of the valves. 



14. Axinaa {Iseptentrionalis, var.) subobsoleta, 



A. testa A. s^tentrionali simili, parum incequilaterali, baud tumida; 

 umbonibus obtusis, latis, satis prominentibus ; cinerea, rufo-cas- 

 taneo varie picta ; epidermide copiosa, sublaminata ; marginibus 

 ventrali et postico valde rotundatis, antice parum producte, dor- 

 sali recto ; sulcis radiantibus subobsoletis sculpta, dorsaliter sa;pe 

 evanidis : intus, marginibus ventrali valde, ant. et pest, parum cre- 

 natis ; lamina cardinis subangulata ; dentibus paucioribus, validis, 

 angustatis ; cicatr. add. antica castanca, callesa ; ligamento sul- 

 cato. Long. '13, lat. • 1 2, alt. 7. 



Hab. Neeah Bay {Swan) ; Shoalwater Bay {Cooper). ' 

 MiddendorfPs shell is figured with much stronger ribs, but 



may have been described from decorticated specimens. 



15. Siphonaria Thersites. 

 S. testa parva, tenui, baud elevata, valde inaequilaterali, dense nigro- 

 castauea, laevi, seu interdum costulis paucis, obtusis, obsoletb, 



