152 Silurian Fossils of Nova Scotia, 



advance of the anterior third, posterior end narrow and abruptly 

 rounded; basal margin slightly curved, and impressed posterior 

 to the centre ; posterior cardinal line straight but gradually de- 

 clining ; contour evenly convex. Surface concentrically striated, 

 shell thick. 



This shell resembles the T. machceriformisj bnt the anterior 

 end is proportionally longer and more regularly round, the pos- 

 terior narrower and more attenuated, and the convexity of the 

 shell much greater. It is much smaller and proportionally more 

 elongated than the T. nasuta of the Trenton Limestone. 



22. Tellinomya angustata. N. sp. 



Shell elongate, narrow elliptical, more than twice as long a& 

 wide, beaks fully one third from the anterior end. The anterior 

 and posterior ends similar and equally rounded ; basal margin 

 regularly curved without indentation or sinuosity. Surface even- 

 ly convex and very finely concentrically striated. 



23. Leptodomus, (Sanguinolites,) aratus. N. sp. 



Shell rhomboid-ovate, ventricose, beaks at the anterior third of 

 the valve, incurved and pointed forward, umbones gibbous, a 

 slight depression from the umbo directly to the base of the shell 

 leaving a slight impression in the central margin ; posterior slope 

 sub-angular, the angle not defined ; anterior slope with a defined 

 angular ridge which borders a large cordiform liinette ; anterior 

 sharply rounded ; basal margin nearly parallel with the hinge 

 line, curving upwards at the posterior extremity, and somewhat 

 obliquely truncated from the cardinal line. Cardinal line straight 

 posteriorly, with a wide and deep ligamental area. Surface 

 marked by strong unequal ridges and furrows parallel to the 

 basal margin, which become obsolescent on the posterior cardinal 

 slope. 



It is scarcely possible to refer any fossil with satisfaction to the 

 genera Sanguinolites or Leptodomus of McCoy, since the group- 

 ing of species under these names appears to us to comprise a 

 heterogeneous assemblage in either case. Our shell corresponds 

 in its external features with Leptodomus costellatus of McCoy, so 

 far as the general form, surface markings, ligamental area, etc. 

 and is doubtless generically identical with that shell. 



