EEOM THE LTSTEEEIOR OOLITE. 523 



Nttcitla. mrcrFOEMis, n. sp. Plate XVIII. figs, o, 5a. 



Shell small, nearly spherical, oblique, very convex. Umbones 

 extremely large, anterior, but curving round regularly, and be- 

 coming proximate and subacute at their extremities. Lunule bounded 

 by a rounded circular groove, within which the surface swells again, 

 so that the anterior side, the lunule, and the side of the umbo are in 

 one flat plane. Posterior and inferior margins meeting in a some- 

 what produced rounded corner, the ventral margins of the two 

 valves meeting perpendicularly. Surface with irregular growth- 

 lines, and four or five much deeper depressions, so that it appears 

 concentrically swollen in three or four curves. 



Locality. Dundry. One specimen in the Bristol Museum. 



Dimensions of both valves, 6 lines long by 5 wide, and 5 deep. 



This may possibly be only an extreme variety of the preceding 

 form, although its prominent lunule and spherical shape seem to 

 individualize it very strongly. 



Isoaeca capitalis, n. sp. Plate XVIII. fig. 6. 



Shell massive, very convex, and transverse. Umbo extremely 

 swollen, incurved, and rounded, situated at one fourth the diameter 

 from the anterior side, and nearly proximate. Hinge rather less 

 than the width of the shell, bluntly angular in front, and covered with 

 very numerous oblique teeth, which are longest on the anterior side. 

 Hinge-area very narrow, bounded behind by a strong ligamental 

 ridge, which curves from the umbo to the posterior end of the hinge. 

 Side margins obliquely divergent ; antero-inferior corner moderately, 

 and postero-inferior corner exceedingly convex ; inferior side nearly 

 straight. Surface very convex, except at the superior corners, 

 covered by occasional strong growth-ridges, and by multitudinous 

 microscopical close flat rays. 



Size of each Valve. — Length 1| inch, width 2± inches, depth 

 1 inch, 



This shell, of which there are four specimens at Jermyn Street, 

 from the Parkinsoni-zone of Hodborough, is very similar to Isoarca 

 transversa, Quenst. Jura, t. 78. fig. 9, which, however, is less trans- 

 verse, more rounded in front, and has a more anterior umbo. i~. 

 ovata, Laube, ' Bivalven von Balin,' t. 3. fig. 1, still more nearly ap- 

 proaches it ; but its posterior margin is much more evenly rounded, 

 and the teeth are smaller in the front part of its hinge. 



Isocaeca texata, Miinst., sp. Plate XVIII. figs. 7, 7a. 



1832. Isocardia cordiformis, Zieten, Verst. Wiirtt. 62. fig. 3. 



1832. Area obliquata, Zieten, Verst. Wiirtt. t. 70. fig. 2. 



1836. Pectunculus texatus, Miinst., Goldf. Petr. Germ. 1. 126. fig.l. 



1836. Isocardia texata, Miinst., Goldf. Petr. Germ. t. 140. fig. 1. 



1843. Isoarca texata, Miinst. Beitr. z. Petr. vi. 83, t. 4. fig. 18. 



1858. I. texata, Quenst. Jura, t. 78. fig. 11. 



1858. Isoarca cordiformis, Quenst. Jura, t. 93. fig. 17. 



A shell from Nailsworth, in the Jermyn- Street Museum, is almost 



