NATURAL SCIENCES OF PHILADELPHIA. 141 



angular above, and terminating in a rather small, rounded sinus below, the 

 form of which is well defined by a sudden curve in the lines of growth on a 

 broad spiral ridge round the edge of the pillar lip ; outer lip very thin ; inner 

 lip thinly spread over the extremely tortuous columella. Length -77 inch ; breadth 

 •58 inch ; length of aperture -61 inch, breadth of do. -30 inch; apical angle 

 convex, divergence 105". 

 Locality and position. Moreau Trading Post and Fox Hills, No. 5 of the series. 



Xylophaqa elegantula. 



Shell small, globose-cordate, very ventricose ; posterior rounded and closed ; 

 anterior having a profound angular notch in the under part, so as to produce a 

 very large hiatus extending more than one-third the length of the shell back 

 from the buccal extremity, and above the middle; beaks elevated, gibbous, very 

 strongly incurved and placed a little in advance of the middle ; surface orna- 

 mented by small regular concentric wrinkles and very fine lines of growth ; the 

 wrinkles are rather obscure on the posterior part of the shell, but upon reach- 

 ing a narrow sulcus, which passes from the beaks to the base, a little in advance 

 of the middle of the shell, they suddenly become more distinct, and are deflected 

 upwards nearly parallel with the vertical margins of the hiatus, near which they 

 again become very fine and regular; on passing upon that portion of the valves 

 extending out in front over the hiatus, these fine wrinkles are deflected, almost 

 in a horizontal direction, and suddenly enlarged, but rapidly diminish, and 

 converge as they pass round the anterior extremity. 



On the cast, the mesial sulcus extending from the beaks to the base is very 

 narrow but deep and sharply defined. At the points where the concentric 

 wrinkles cross this sulcus or groove, it is distinctly punctate. Further back, a 

 rather distinct carina extends from the back part of the beaks obliquely back- 

 wards and downwards nearly to the base of the shell ; immediately behind 

 this ridge, the posterior part of the cast is suddenly compressed, and faintly 

 marked by a large leaf-like muscular impression. The pallial impression is 

 narrow, stands nearly vertical, and extends more than halfway up to the beaks 

 between the mesial sulcus and posterior carina. 



Locality and position. Muscle shell River, where it was found embedded in 

 fossil-wood, — formation No. 4. 



Xylophaga Stimpsoni. 



Shell ovate, gibbous in front, and cuneate behind ; posterior end obliquely 

 subtruncate above, round below, nearly or quite closed; anterior having a dis- 

 tinct angular notch below, which forms a large hiatus extending back one- 

 fourth the length of the skull and upwards above the middle ; base and dorsal 

 margins parallel ; beaks not much elevated above the dorsal edge, pointed at 

 the apex, and strongly incurved. Surface marked by distinct, regular con- 

 centric wrinkles, and extremely fine lines of growth. The wrinkles are more 

 obscure on the posterior part of the shell, but on crossing a narrow sulcus (in 

 the cast) that passes from the beaks to the base, they become more distinct, 

 and curve gracefully upwards nearly parallel with the edge of the hiatus; on 

 passing forward upon the upper anterior part of the valves extending out over 

 the hiatus, they are suddenly deflected in a horizontal direction and become 

 stronger, but rapidly diminish and converge in passing round the anterior ex- 

 tremity. 



On the cast, the mesial groove extending from the apex of the beaks obliquely 

 downwards and a little backwards to the base, is narrow but well defined. A 

 little in advance of this, and nearly parallel with it, a fainter impressed line 

 passes from the beaks to the base. About halfway between the mesial groove 

 and the posterior end of the shell, another deep, but broader, groove extends 

 from the posterior side of the beaks obliquely backwards nearly to the lower 

 part of the anal extremity; behind this the narrow oval posterior muscular 

 impression is seen faintly indicated near the border. 



Although resembling the last in its style of ornament, this is a very distinct 



1857.] 



