16] 



i 



lines can be seen beneath the surface of the area, as if it were penetrated 

 by internal small tubes, passing from the teeth towards the cardinal edge, 

 and inclining a little towards the beak ; umbo moderate, but in the most 

 ventricose specimens, the umbonal region is so exceedingly tumid, that it 

 projects a little over the hinge line ; beak not distinct from the cardinal 

 edge. Dorsal valve with a curvature corresponding to that of the ventral, 

 leaving but a thin space for the animal ; area half the size of that of the 

 opposite valve, and forming an obtuse angle therewith. 



There are three or four spines on the cardinal edge of the ventral valve, 

 rarely preserved. They incline outwards at an angle between 40^ and 

 50^. I have seen no specimen with all the spines preserved, but it seems 

 probable that those nearest the beak are the shortest. 



Surface with fine, closely arranged, convex ribs, eight to ten, on an 

 average in the width of one Hne, increasing both by bifurcation and inter- 

 stitial addition, and crossed by exceedingly fine concentric striae, of which 

 there are between thirty and forty in one line. The ribs are slightly flex- 

 uous and of a very uniform size. In some specimens, the ventral valve 

 exhibits an obscure mesial sinus extending from the beak to the front 

 margin. 



The form and dimensions of this species vary but little from the des- 

 cription above given. The cardinal angles are usually more acute and 

 extended than they are in the two specimens figured ; and in such 

 instances the form closely resembles that of G. acutiradiata, Hall, Pal., 

 N.Y., vol. 4, p. 20, fig. 56. The spines also in these two species 

 diverge at about the same angle, and, according to the descriptions, the 

 surface characters are nearly the same. In the description of C. acuti- 

 radiata, no mention is made of the existence of teeth or crenulations 

 on the area ; it may be because the specimens were not in a condi- 

 tion to exhibit them if they really do exist. Should this character be yet 

 discovered in the New York species, perhaps the two ought to be united. 

 0. hemispherica, Hall, and 0. arcuata, Hall, belong to the same group, 

 but are considerably larger. I have compared C. Melonica with speci- 

 mens of C striatella, Dalman, from the Island of Gotland, Sweden ; and 

 also with 0. Nova-Scotiea^ Hall, from Arisaig, Nova Scotia, and find it 

 perfectly distinct from either. 



The number of strias on specimens of the average size is usually 

 between seventy and eighty, but as many as 130 have been counted. 



Locality and Formation. — This species occurs abundantly at Little 

 Gaspe ; in the Gaspe limestone. No. 8. 



Collectors.— W. E. Logan, R. Bell. 



