WHITEAVES.] DEVONIAN FOSSILS OF MANITOBA, ETC. 319 



Shell discoidal, composed of three or four rounded volutions, which 

 appear to be coiled on nearly the same plane and are in contact through- 

 out their entire length, but partially separated on both sides by a deep 

 suture and almost free : umbilicus wide and open, exposing all the inner 

 whorls. Outer volution very slightly expanded at the aperture, in the 

 largest specimen collected (the one Kgured) : its periphery encircled with 

 a narrow slit band, in the form of an obtuse central carina ; aperture 

 circular. 



Surface very minutely, closely, and transversely but somewhat obliquely 

 costulate on each side of the slit band : test extremely thin. 



Maximum diameter of the largest specimen collected, forty millimetres : 

 diameter of its aperture, sixteen mm. 



Pentamerus Point, Lake Manitoba, J. B. Tyrrell and J. F. Whiteaves, 

 1888 : the specimen figured. Dawson Bay, Lake Winnipegosis, at 

 Whiteaves Point (one specimen), at a small island half way between that 

 point and Salt Point (one specimen), at Beardy Island (one specimen) 

 and at the south end of Rowan Island (four specimens) ; J. B. Tyrrell 

 and D. B. Bowling, 1889. 



Of the eight specimens collected, one is small and very imperfect but 

 wholly testiferous, four are casts of the interior of the shell, with portions 

 of the test preserved on either or both sides of the slit band, but not 

 actually upon it, and the rest are sharply defined moulds of the exterior 

 of the shell. The nuclear volution is not preserved in any of these speci- 

 mens, and in casts of the interior the slit band appears as a narrow rounded 

 and not much elevated spiral ridge with a linear groove on each side of it. 



As it is doubtful whether these few and imperfect specimens are or are 

 not actually conspecific with P striata, it is thought desirable to designate 

 the former by a local and provisional name. The only differences, how- 

 ever that the writer has yet been able to detect between P. Manitohensis 

 and P. striata are that the former appears to attain to a much larger size 

 than the latter, and to be slightly expanded at the aperture in the adult 

 state. 



In the Geological Magazine for May, 1891, Mr. R. B. Newton proposes 

 to change the name Porcellia of Leveille (1835) to Leveillia, on account 

 of the circumstance that that of Porcellia had been given by Latreille in 

 1804 to a genus of Isopods. Still, the substitution of a new name for 

 one with which paL-eontologists have become familiar by long usage, seems 

 to the writer a greater inconvenience than would result from the use of 

 two similar but not identical names, in such widely different divisions of 

 the animal kingdom as the Mollusca and Arthropoda. 



December, 1892. ^ 



