COLOSTRACON. 31 



ColostraCOn, gon. nov. 

 (xuXof, ilecurtalus ; oarpaKoi', testa.) 



Testa inverso-conica aid decurtato-fusiformis, tenuis ; spira valde depressa, plana 

 aid immersa : anfractus qiiaterni qidni vel sent, conferiiin cui/rohifi, a laierihus planaii 

 et plus minusve insimiati, postice truncati acute angulati ct ad aiujidum aliquunto cari- 

 nati, sidura pcrspicua dlvisi ; idtinms antice si non in canaUciduni at in rostrum tamen 

 porrectiis : superficies lineis incrcmenti notata et per partes spiraliter striata aid leviter 

 sulcata : apcrtura rectiuscula, coartata, testce longitudini adeerpians, ante medium 

 dilatata, antice angustata ; columella arcuata, edeniula, prohngata ct pmuliim con- 

 torta, hdiio tcnui rcfiexo modice ohtccta, pieranguste rintiduta ; hdiruin simplex. 



Shell inversely conical or decurtate-fusiform, thin ; spire greatly de- 

 pressed, plane or immersed : whorls fonr to six, compactly convolute, later- 

 ally flattened and more or less insinuate, behind truncate, acutely angulate 

 and at the angle considerably keeled, separated by a distinct suture; the 

 body-whorl produced in front into what must be styled at least a beak, if not 

 a proper canal : surface marked with lines of growth and on portions spirally 

 striated or lightly grooved : aperture rather straight, contracted, as long 

 as the entire shell, Avidened before the medial line, narrowed in front; 

 columella arcuate, without folds, prolonged and somewhat twisted, moder- 

 ately covered by the thin reflexed labium, very narrowly fissured ; lal^rum 

 simple. 



Absence of folds from the columella and the presence of transverse stri- 

 ations upon their exterior exclude these shells from Cylindrites, but suggest 

 their classification under Actccom'nu. To the latter genus they would cer- 

 tainly seem to belong, were it not that a short but distinct anterior beak 

 or canal is present in our typical species. And though from imperfection 

 of the specimens it cannot positively be asserted that a similar beak occurs 

 in the second species described by us, nor in that refigured from Fraas, 

 the combination in botli of like peculiar and striking characters leads to 

 the inference from analogy that the Ijcak can hardly be wanting in perfect 

 examples. 



Of the species of Actcconina known to us from actual specimens, not one 

 shows any indication of a beaked or chainielled aperture. Loriol's figure of 

 his A. Davidsoni, etage portlandien (Monogr. des liltages superieurs de la 

 Formation Jurassique de Boulogne-sur-Mei", p. 44, PI. vi, figs. 8, 9, 1873), 



