THE FAUNA OF THE ST. JOHN GROUP. 49 



Paradoxicles beds, and noue of them occiir as low down as the Olenus beds ; hence it may 

 be that the special forms hereinafter described are peculiar to the primordial fauna. 



The modern genus, Cuvieria, possesses a septate shell, which has some features in 

 common w'ith Camerotheca, but the lower part of the body-cavity is more ventricose, and 

 the lower chambers formed by the septa at the apex (if such ever existed) are broken off or 

 from other caiise, are wanting. 



In order to make more complete the description of these pteropods, I introduce, from 

 Bulletin No. 10 of the United States G-eological Survey, the account of these species, 

 reversing the use of the terms dorsal and ventral. 



^& 



Hyolithes (Camerotheca) Danianu;^. (Plate VI. Figs. 1, la, h and c.) 



Hi/olilhex Danianus, U.S. Geol. Surv., Bull. 10, p. 20, PI. II. Fig. 1, la and h. 



The form is that of an extremely elongate, rounded, subtriangular pyramid, that, in 

 some examples curves a little to one side as it becomes gradually attenuate toward the 

 apex. Transverse section semi-elliptical, moderately convex on the dorsal side, and still 

 more on the ventral. Dorsal face flattened and almost concave along the centre, rounding 

 upon each side to the somewhat rounder lateral angles. Ventral face not very strongly 

 convex transversely. Form of aperture unknown. 



An associated operculum is broad-oval, or subcircular in general form. The side corres- 

 ponding to the dorsal side of the shell curves regularly, but is not as convex as the opposite 

 side. The umbo (or nucleus) is situated about four fifths of the distance from the ventral 

 margin, and from it two low rounded ridges extend laterally toward the rounded angles 

 formed by the junction of the ventral and dorsal edges of the operculum. .Tust in front of 

 these ridges a slight depression exists, also a depressed area back of the umbo, or towards 

 the ventral margin ; the inner side shows also a sharp, short, elevated ridge between the 

 dorsal margin and the position of the umbo on the outer surface. The general body of the 

 shell of the operculum appears to be quite thin. 



Surface of the shell marked by transverse, concentric undulations of growth that arch 

 slightly forward on the dorsal side. Outer surface of the operculum marked by fine, con- 

 centric strire, and very fine, somewhat obscure, radiating strife : inner surface with fine, 

 slightly irregular, radiating lines or strin'. This opercvrlum w^as not found in the mouth 

 of the shell. 



There is a considerable range of variation in the form of the shell of this species. In 

 some the flattening of the dorsal side is lost, and only a convex surface is shown, and the 

 ventral surface has a narrow, longitudinal line on each side of the centre. The curvature 

 of the shell also varies considerably. A number of specimens of the operculum are asso- 

 ciated with the shells, but none were observed in place, before the mouth of the shell. 



Mr. Walcott says of the Ilartt collection " that one unusually curved shell, having a 

 nearly round section, w^as labelled Orthocems, n. sp., by Professor Hartt, as traces of what 

 appear to be septa are shown. The distances between the septa-like partitions are un- 

 equal, and in other specimens this is seen to be owing to the filling of cracks across the 

 tube. — This species recalls Hyulithes cinckis, Barrande. Syst. Sil. Bohème, Vol. III. Plate 

 IX, Figs. 8-12. — Formation and Locality. Cambrian, St. John formation, Ratcliffs Mill- 

 stream, N.B.'' 



See. IV., 1SS5. 7. 



