O THE GASTROPOD GENUS YVANIA 



respect this genus resembles Aviculopcctcn among the pelecypods and Pro-- 

 ductus among the brachiopods, except that the present status of Pleurotomaria 

 is much more unsatisfactory, both on account of the extensive range of its 

 representatives throughout geologic time and because the work which has 

 been done upon its subdivision is less well understood. 



The only discussion of the Heurotomariidae in American literature 

 which is at all comprehensive is that by Ulrich in the Paleontology of Min- 

 nesota. 1 He is primarily concerned with lower Paleozoic forms but proposes 

 two new Carboniferous genera and discusses others confined to or represented 

 in these strata. He also lists those characters which in his opinion may be 

 employed in making generic discriminations. 



The most extensive consideration of Carboniferous forms is that by 

 de Koninck in his description of the Belgian Carboniferous fauna. 2 His 

 forms are grouped in eleven genera, most of them new and rather unnatural 

 systematic units as arranged by him, which have received almost no recogni- 

 tion from later writers. However, several of these genera are potentially 

 useful ; among them is that for which he proposed the name Baylea. It is 

 the purpose of this paper to redefine this particular genus, establish it as a 

 natural unit, and describe the American species that may be referred to it. 

 several of which are new. 



Genus YVANIA Bayle (BAYLEA de Koninck) 



In 1883 de Koninck proposed the name Baylea for a group of ten species 

 of Pleurotomariidae, with Baylea yvanii Ch. Leveille as the type. 3 This name 

 however was preoccupied by Bayleia Munier-Chalmas 1873. and Yvania, a 

 name proposed in manuscript by Bayle, was substituted by Fischer without 

 emendation in 1885. 4 



A translation of de Koninck's original description of the genus is as 

 follows : 



"Shell conical, turreted, spire in form of steps the vertical and horizontal parts of 

 which join each other at a right angle. The band of the sinus, relatively large, is 

 situated on the lower (upper) plane part and horizontal to the turns of the spire; it 

 lies along the external angle of these turns and is limited on the opposite side by a 

 fine slightly elevated carina. The upper (lower) part of the last turn is very convex 

 and ornamented with a great number of shallow spiral furrows, which largely occupy 

 the median part. The aperature is large and has the form of an inverted escutcheon: 

 its columellar border is thin, and being extended lenthwise, gives rise to the formation 

 of a little umbilical dimple. 



1 ITlrich E. O. and Scofield, W. H., The T.ower Silurian Gastropoda of Minnesota 

 Geol. and Nat. Hist. Survev of Minnesota, vol. 3. pt. 2, pp. 946-960, 1897. 



2 De Koninck. U G., Faune de calcaire Carboniff-re de la Belgique: Annales Mus, 

 Roy, Hist. Xat. Belg., vol. 8, pt. 4, 1SS3. 



3 Op eit., p. 6S. 



4 Fischer, P., Manuel de Cbonchyliologie, p. 851. 1885. 



