Prof. F. M'Coy on some new Mountain Limestone Fossils. 175 



uadulatory interruption of the ridges at the place mentioned, 

 and in being shorter, and the greatest gibbosity of the shell 

 being along the anterior boundary of the posterior slope — it 

 being much nearer the anterior end, and the posterior portion 

 being compressed in that species, in which also the greatest gib- 

 bosity is nearer to the dorsal margin, giving a much less tumid 

 character to the lower part of the valves. From the S. sulcatus 

 it diflFers in the wrinkles not uniting into few large wrinkles in 

 passing to the posterior slope, &c. 



Rare in the carboniferous limestone of the Isle of Man ; not 

 uncommon at Lowick, Northumberland. 



{Col. University of Cambridge.) 



Leptodomus costellatus (M'Coy). 



Sp. Char. Oblong, very tumid, width three-fifths of the length, 

 depth of both valves about equal to the width ; anterior and 

 posterior lunettes large, defined ; beaks large, tumid, incurved, 

 terminal, anterior side obtuse, subtruncate, slightly oblique be- 

 neath them ; a small sinus in the ventral margin close to the 

 anterior end, from which a narrow concavity extends nearly 

 to the beaks close to the anterior edge; hinge-line nearly as 

 long as the shell, with a slight upward curvature ; posterior end 

 wide, slightly oblique, subtruncate, rounded j ventral margin 

 strongly convex behind the sinus; posterior slope abruptly 

 compressed, smooth, or with a few lines of growth parallel 

 with the margin, divided nearly in the middle by a small fur- 

 row from behind the beaks; sides marked with numerous 

 small, regular, close, narrow, rounded ribs parallel with the 

 margin (about four in the space of 2 lines) ; these abruptly 

 disappear on reaching the edge of the posterior slope, and 

 unite on the anterior edge in front of the sinus in parcels of 

 two or three to form a row of short thick wrinkles on that 

 part. Length 1 inch 4 lines, width 10 lines, depth 10 lines, 

 width of posterior lunette li line. 



I long imagined this to be the Hiatella sulcata of Fleming, 

 but it seems Dr. Fleming agrees with Prof. Phillips as to that 

 being identical with the Sanguinolaria sulcata of the latter. The 

 present species differs from the Sanguinolites sulcatus (PhUl. sp.) 

 in its thin shell, short inflated form, want of the thick internal 

 cardinal ridges, the more regular sharp ribs on the sides, and 

 their uniting into large wrinkles on the anterior instead of the 

 posterior end. 



Common in the carboniferous shales of Craige near Kilmai'- 

 nock ; carboniferous shales near Glasgow ; in the shaly beds of 

 Lowick, Northumberland. 



{Col. University of Cambridge.) 



