COLOSTRACON SINUATUM. 33 



views are given, which leave the character of that part doubtful. No folds 

 are represented upon the columella, and if better preserved specimens should 

 show the base to be rostrate, the sum of characters would obviously require 

 that the species should be assigned to our proposed group. 



The comments of Meek* and others, based chiefly on imperfect figures, 

 have been charged with adding to the confusion which already existed in 

 the family Actoeonidce ; and there seems to be no hope of bringing order out 

 of that confusion, except by the critical study of its representatives from 

 fuller series than are to be found in American collections. It is only from 

 inability to classify our specimens under any of the recognized subdivisions 

 of this unsettled family, that we have ventured to propose in it a new group. 

 We regret the necessity of drawing conclusions from material so scanty. 



Colostracon sinuatum, sp. nov. 



Plate III, flits. 3 a, b, c. 



Testa tenuissima, decurtato-fusiformis, a latere transversim late insinuata : spira 

 maxime depressa, ah apice cequaMter xrrf nunime ad peripheriam declivis ,• anfractus 

 circiter sex, postice truncati et angukcti, ad angulum acute carinati, sidura lineari 

 perspicua sejuncti ; vMmus in rostrum breve productus : superficies lineis incrementi 

 fortioribus flexuosis signata, et mile sinum lateralem xit/ei* exiguis cincta : apertura 

 anomala, ml sinum angustata ; lithium tenue, super columellam ezpansum, antice in- 

 crassatum ; columella paulum contorta, rimulam umbUicarem exhibens. 



Shell very thin, decurtatc-fusiform, upon the hinder part of the side 

 transversely widely insinuate : spire exceedingly depressed, regularly but 

 very slightly sloping from apex to circumference ; whorls about six, truncate 

 and sharply angled behind, acutely keeled at the angle, divided by a distinct 

 linear suture; body-whorl produced in front into a short beak: surface 

 stamped with rather strong flexuous lines of growth, and before the lateral 

 sinus encircled by small shallow grooves: aperture of peculiar shape, nar- 

 rowed at the sinus; inner lip thin, thickened in front, outspread upon the 

 columella, which is somewhat twisted and shows a slight umbilical chink. 



A single specimen, with test nearly complete. Length, IS nun. ; width. 

 at keel, 10 mm. 



Figure 3 c represents upon the Hat posterior side of the aperture succes- 



* Remarks on the Family Actseonidae, with Descriptions of some nen Genera and Subgenera. Am. 

 Jour. Science, (2.) XXXV, pp. 84-94, 1863. 



