146 AMERICAN JOURNAL 



the sides. Shell very thick, solid, muscular impression deeply 

 impressed. Long. -56, lat. -52, alt. -20 in. Defl. apex 120°. 

 Number examined, 6 specimens. 



Soft parts unknown. Sitka, 10 fms. shelly mud, dead. 



In the absence of the animal it is impossible to refer this sin- 

 gular form definitely. Its affinities appear to be with Grypto- 

 branchia, as far as can be judged, except that the sides are com- 

 pressed ; it resembles a little Nacella instabilis, a much larger and 

 more elevated shell, from California. 



Spurious Species. 

 f? Lepetajmntarenensis, Trosch. (ex Morch),Wiegm. Arch. 1860. 

 iSyn. Lepeta jmntarence ! Morch, Mollusk-fauna Centr. Am. 

 iMalak. Blat. Dec. 1860, p. 175, No. 215. 



Sp.ch. — " Testa ovalis, apice elevata excentrica, intus lactea, 

 extus flavescens ; lineis exilibus, radiantibus et conccntricis sub- 

 aequalibus, crebrerrimis ; confertim decussata intersection ibus 

 nodosis. Margine integro. Facies L. ccecce, Mulleri. Long. 6, 

 lat. 4, alt. 2 mill. Punta Arenas (Pacific coast Central Amer.) 

 1 specimen. Differs from L. cceca in the very thick and strong 

 concentric lines and delicate radiating lines." 



This shell is probably not sl Lej^eta, its habitat being tropical; 

 it may be a Scutellina^ or even an Acmoea ; it is quite impossi- 

 ble to determine the generic affinities from the shell alone. 



Genus PILIDIUM Forbes. 



Syn. PiUdium [fulvum), Forbes, Athenaeum, Oct. 6, 1849, p. 

 1018. Forbes and Hanley, Br. Moll. vol. ii, p. 440, 

 1849. Wood, Ind. Test. pi. 38, fig. 83. 



lothia, Gray (not Forbes), Syst. An. figs. ; Moll. An. 

 1854, p. 93 ; Guide Moll. p. 172. H. and A. Adams, 

 Gen. Rec. Moll. (Fam. Tecturidae), vol. i, p. 461. 



PiUdiiwi, Stimpson, Check List E. C. Shells. 



iScuteUma, Chenu (pars), Man. de Conchy. 



Not PiUdium, Midd. (P. cojnmodum), Sib. Reise, 1851, 

 p. 214 = ? Velutina, sp. jun., nor 



PiUdium, Stimpson, Shells of N. Eng. = Lepeta, pars, 

 nor 



lothia, Forbes = err. typ. for Lottia. 



(The circumstances under which this genus was named having 

 been a subject of discussion, and few naturalists in this country 

 having the opportunity of consulting the newspaper report in 

 which it was originally published, the extract is given verbatim.) 



