360 



The squares formed by the stolons are on an average li lines on the 

 side. The largest sized squares that can be made out in .R. occidentalis 

 are 1 line on an average, and in general they are somewhat less. 



Locality and Formation. Mingan Islands ; calciferous formation. 



Collector. J. Richardson. 



RECEPTACULITES ? ELEGANTULUS. (N. sp.) 



Fig. 347. 



Description. This appears to be an elongate sub- cylindrical species, 

 several inches in length, about one inch in diameter and probably taper- 

 ing or more or less rounded at each end. The best specimen is a frag- 

 ment of nearly half of the cylinder split in two longitudinally and empty. 

 The drawing is made from a gutta-percha cast of the interior, and is too 

 straight, the original being slightly undulated. The whole of the inner 

 surface is covered with obscurely rhomboidal elevations arranged in oblique 

 rows crossing each other at an angle of about 45. These elevations leave 

 corresponding rhomboidal pits in the gutta-percha cast represented above. 

 There are on an average four or five pits in the length of two 

 lines. The fossil is imbedded in a finely granular magnesian limestone, 

 and, although the thickness of the, wall can be very clearly made out, yet 

 the tubes which ought to be apparent, if it be a true Receptaculites, are 

 not visible. Supposing them to exist, they would be, in this species, very 

 slender, and in this kind of rock all delicate structure is usually destroyed. 

 The thickness of the wall is only two lines, and therefore, the tubes would 

 be less than two lines ; while their diameter, if in proportion to other species, 

 would be one-eighth of a line or thereabout. 



It is referred to Receptaculites provisionally. 



Locality and Formation. Mingan Islands ; Calciferous formation. 



Collector. J. Richardson. 



GENUS EUCHASMA. (N. gen.) 



G-eneric Characters. The only species of this genus known to me is 

 strongly convex triangular, inequilateral, equivalve, subcordiform. The 

 posterior ? extremity is flat and gaping the whole length. The anterior ? 

 extremity is rounded-angular, and seems to be gaping also ; but no speci- 

 mens have been procured with this part perfect, and, therefore, this point 

 remains doubtful. The hinge line is short, and seems to have an external 

 ligament. When the flat side is ground down gradually, it is found that 

 just below the umbones the shell of both valves has a large rounded pro- 

 tuberance on the inside. These leave an impression in the cast of the 

 interior just behind the umbone. 



