TIIK GASTROPOD GENUS YY.WIA 9 



"Dimensions. — The length of the largest specimens rarely exceeds 40 mm, and the 

 transverse diameter 25 mm 



"delations and Differences. — The species which 1 propose to unite in this group 

 have for principal character the existence of the hand of their sinus on the horizontal 

 part and below (above) the turns of the spire; this hand is in consequence invisible 

 when the shell is seen in profile. In the shells of all the othct genera of the same 

 family, except on those ol the genus Luciella in which it is found situated on the upper 

 (lower) part of the turns, it is perfectlj perceptible, in this same position, at least on 

 the last turn. No other genus possesses, however, a form so perfectly turreted as that 

 of the group which is here in question and which has for type Baylea (Pleurotomana) 

 yvu hi, Ch. Leveille. 



"Geologic Distrii ution. — Nearly all the species of this genus belong in the Car 

 boniferous terrain in which it becomes extinct. In Belgium two of these species exist 

 in the lower heds of the terrain; two others have been discovered by Mr. Ed. Dupont 

 in the middle beds. and. finally, two species are found in the upper heds. One species 

 the middle beds has been figured in Ireland bj Mr. F. McCoy and one other from 

 the upper beds has been described by J. Phillips from Yorkshire. I have observed one 

 or two in the middle beds of the Devonian limestone in the neighborhood of Vise." 



As may be seen by the above description, the essential feature upon which 

 this genus is based is the presence of the slit band mi the upper surface and 

 adjacent to the prominent angle of the volution. The turreted form of the 

 spire, which is emphasized by de Koninck in his generic description, and the 

 meeting of the upper and outer sides of the volution at a right angle are by 

 no means constant characters, and the description is misleading in this respect 

 as may he seen when the illustrations of de Koninck's ten original species 

 are examined. 



Kokeir held that this genus was an arbitiary group and pointed to a 

 series connecting the type species, which he considered simply an extreme 

 form of development, with species described by de Koninck as Ptychomphalus 

 and M ourlonia. When it is considered, however, that these latter genera have 

 no meaning as employed by de Koninck and served only to hold those species 

 that he could not place elsewhere, Koken's argument loses its significance. 

 Perhaps the species referred to by him should have been placed originally in 

 the genus Baylea. That de Koninck did not place them there is without 

 significance as his grouping i-* in so many respects unnatural. 



In the group of species described in this paper the slit band is located 

 upon the upper slope of the whorl and adjacent to the angle, hi five of the 

 -;.ecies an additional feature serves to sharply distinguish them from most 

 other Carboniferous representatives of the Pleurotomariidae, namely a con- 

 spicuous backward curvature of the lines of growth adjacent to the suture. 

 De Koninck's figures of hi- genotype show that this species also was orna- 

 mented by faint growth lines which curved slightly backward in the vicinity 



5 Koken, K .. Deber iii>- Entwickelung der Gastropoden vom Cambrtum blfl zur Trias; 

 \". Jahrbuch, Bid. 6, i>. 



