918 PELECYPODA. [Eulaniellibranchia. 



brown. Colour white, brownish where the epidermis is left ; some- 

 times light flesh-colour. Interior dirty-white, dull. Margins thin, 

 smooth. Hinge delicate ; right valve with a high and narrow anterior 

 and stronger bifid cardinal tooth ; left valve with the posterior 

 cardinal tooth oblique, lamellar, the anterior triangular, high, and 

 deeply sulcate. Ligament rather short, conspicuous, external. Ad- 

 ductor-scars subequal, oblong, continuous with the simple pallial line. 



Diameter Ant. -post.. 22 mm. ; dorso-ventral. 21 mm. : thickness, 

 12mm. 



Type in the British Museum. 



Hab. Bay of Islands ; near Channel Island, Hauraki Gulf, in 

 25 fathoms ; Auckland Harbour, on mud-banks near low-water mark ; 

 Banks Peninsula ; Chatham Islands ; Kermadec Islands (Captain 

 Bollons). Also Tasmania and Australia. 



Fossil in the Miocene and Pliocene. 



Fam. THYASIRID^J, Ball. 

 Cryptodontidoe. 



Animal without siphons, the foot long, vermiform, with a distal 

 swelling. 



Shell small, usually thin, subglobular, the posterior end furrowed, 

 without a lunule. ligament partly external ; hinge edentulous or with 

 cardinals and laterals. 



Genus 1. THYASIRA, Lamarck, 1818. 



Thjiasiru, Lamarck, A.s.V., v, 1818, 492 (in synonymy). Type : Tettina 

 flexuosa, Montagu. Thi/ntira, Jeffreys, 1839. Bequania, Brown, 1827. 

 Axinus, Sowerby, 1821 ; not Axina, Kirby, 1817. Cryptodon, Turton, 

 1822. Clausina, Jeffreys, 1847 ; not of Brown, 1827. Ptychina, Philippi. 

 1836. M<-i//i.rinus, Brugnone, 1881. Conchocele, Gabb, 1866. Schizo- 

 thcBnts, Locard, 1896 ; not of Conrad, 1853. 



Animal with the mantle-borders thick, without siphons ; foot very 

 long and thin, nearly cylindrical, with an oval swelling at the end : 

 visceral mass with arborescent excrescences. 



Shell thin to subsolid, subglobular, earthy ; beaks turned forward : 

 posterior side furrowed ; lunule absent ; ligament placed in a groove 

 in the hinge-line, partly external ; hinge edentulous, the hinge-margin 

 indented in front of the beaks, which forms a pseudo-tooth ; muscular 

 impressions superficial, elongated ; pallial line simple ; borders of the 

 shell closed, simple. 



Distribution. North Atlantic and Pacific. European seas, Austral- 

 asia. 



Fossil in the Tertiary. 



Vernacular Name. Hatchet-shell. 



KEY TO SPECIES. 



A. Anterior end shorter than the posterior . . . . flexuosa. 



B. Anterior end much longer than the posterior . . . . ofagocnsis. 



