10 Canadian Record of Science. 



tion of a series of small shells of the St. John group, which 

 have a closer affinity for the shell from the Menevian group 

 of Wales, which was the type of Dr. Hicks' genus Steno- 

 theca, leads the writer to infer that Hartt's species acadica 

 is not so close to Hicks' S. cornucopia as is the group of 

 small shells above referred to. Hence it should be distin- 

 guished as a sub-genus, characterized by its subcircular 

 aperture and patelloid form. Probably its nearest relatives 

 now living are not the true limpets, but are among the 

 Fissurellidae, and especially in the genus Parmojihorus, 

 which it resembles in many important particulars. The 

 dimensions of the adult of S. acadica are : height about 7 

 mm., width and length of the aperture equal, and about 12 

 mm. In the young shells, however, the form is quite 

 different, being proportionately higher and much narrower 

 at the aperture ; in both of these respects resembling the 

 small Stenothecse above referred to. 



The internal markings of the shell leave no doubt as to 

 its affinities being with the GJ-asteropocls ; in the young 

 individual herewith figured they are well displayed, the 

 course and extent of the muscular impression being clearly 

 denned : the apex is directed backward and the muscular 

 scar is of an elongated horse-shoe form. 



Except for the absence of an involute apex this sjDecies is 

 not unlike Carinaropsis carinata (Hall) of the Trenton 

 formation; it is compressed near the apex, and expands 

 rapidly toward the aperture in a manner similar to that 

 species, but in the way in which the concentric ridges are 

 added it is comparable with Metoptoma (?) rugosa (Hall). 



It lived in shallow seas along the coast, if one may judge 

 from the species associated with it, and probably was a 

 bottom-crawler. The true Stenothecse appear to have been 

 more varied in habitat, as some are found in company with 

 Hartt's species, and others in finer shales, where they are 

 buried with remains of seaweeds (?), sponges, hydrozoa, etc. 

 A fact in relation to the variation of resembling forms like 

 these is related by Dr. Woodward in his " Manual of the 

 Mollusca," where he speaks of several wide limpets which 

 assume a narrow compressed form when growing on the 



