'. \STROPOI '\ I""-' 



PteUH*plr.l 



Fio. 7. <i, ritOtntpim eojutna Wbitfleld sp , Calclferous formation. Fort Casein. Vermont. Some- 

 what restored view of a good specimen belonging to the D. S. National Museum. The last whorl retain* 

 much of the shell, and shows the char.ni.r- <>r the band and surface markings. 6, c, d, Seelya ventrieotn 



:. n. sp., Calclferous formation. Krt Cassln, Vermont, b, Cast of the Interior of a rather small 

 specimen, collected by Prof. H. M. Seely and presented to one of the authors. The ridge which forms ti..- 

 lower margin of the band Is not prominent enough In the figure, c. Surface of the shell of a species of 

 Seelya from Fort Cassln, x2, taken from an Incomplete specimen belonging to the U.S. National Museum, 

 showing the band and surface markings, d, small portion of the same, xlO, showing the grano-punctate 

 character of the outer surface. This specimen probably belongs to Seelya difficult Wbitfleld sp. Another 

 specimen of S. ventricota In the National Museum is much larger than fc, being 57 mm. high and 40 nun. 

 wide. The last whorl descends very much as In a, and Is marked by five ridges above and Ore below tin- 

 band. 



Plethospirn probably will not prove to be a large genus, yet, as it represents an 

 easily recognized type of shells that moreover continued through a long period of 

 time, it deserves and probably will receive recognition from systematiste. P. cassina 

 \V bitfield sp. is a fine species from the Calciferous rocks of the Lake Champlain 

 region. A second species from that region was somewhat doubtfully identified by 

 W bitfield with Billings' Murchisonia arenaria. For some unaccountable reason 

 W bitfield places both of these Calciferous species under Holopen. A third species, 

 evidently very closely related to the preceding, was called Murchisonia hyale by 

 Billings, who gives it as from "the Cbazy or perhaps the Black River limestone" of 

 Canada East. The same author has described other Lower Silurian shells that may 

 belong here, but, as we have not yet seen his original types, we prefer to postpone 

 their removal from the genera to which he assigned them. Lindstrom's Plturolo- 

 maria ralida, an Upper Silurian species, has a very thick shell and rather too high a 

 spire, but otherwise seems to agree very well with /'/.'//.<>;</>./. Kogarding the 

 following two species, perhaps they are not very good examples of I'lrthonjiini. still. 

 uld be difficult to pick out any important tlirterences; at any rate, we cannot 

 suggest a more fitting disposal of th em at present 



