342 Mr. H. J. Carter on a Large Variety of 



by the reticulate ornamentation of the teeth and the absence 

 of lateral cusps ; the cephalic spines agree ; and the dorsal 

 fin- spines merely differ in the prevailing replacement of a 

 ribbed ornament by series of stellate tubercles. 



EXPLANATION OF PLATE XII. 



Asteracanthus ornatissimus, Yax.Jlettonensis, A. S. Woodw., Oxford 

 Clay, Fletton, near Peterborough. 



Fia. 1. Rigiit ramus of mandible, outer aspect, -Inat. size, t, tuberosity. 



[No. 5.] 

 Fiff. 2. Teeth of upper jaw, series i-iv, upper aspect, nat. size. [No. 4.] 

 Fi(/. 3. Teeth of lower jaw, series o-iv, upper aspect, nat. size. [No. 4.] 

 Fi(/. 4. Hinder tooth, upper aspect, nat, size. [No. 4.] 

 Fiff. 5. Anterior dorsal fin-spine, lateral aspect, f nat. size. [No. 4.] 

 Fiff. 6. Posterior ditto, lateral aspect, | nat. size. [No. 4.] 

 Fiff. 7. Cephalic spine, lateral aspect, f nat. size. [No. l.J 

 Fiff. 8. Ditto, upper aspect, f nat. size. [No. 1.] 

 Fiff. 9. Tooth of (?) series iii, upper aspect, nat. size. [No. 3.] 

 Fiff. 10. Two transversely-divided teeth of series iv, upper aspect, nat. 



size. [No. 3.] 

 Fiff. 11. Hinder tooth, upper aspect, nat. size. [No. 3,] 



(The numbers refer to the Catalogue of the Leeds Collection.) 



XLIV. — Description of a LargeVariety o/Orbitolites Mantelli, 

 Cart.., from the West Bank of the River Irraivadi^ in the 

 Province of Fegu^ Burma, about 36 miles above Prome. 

 By H. J. Caetek, F.R.S. &c. 



Oi'bitolites Mantelli, var. Theobaldi, n. var. 



Discoid, slightly undulous, flat, thin. Consisting of a well- 

 marked central plane of ?-spheroidal cells in juxtaposition, 

 bordered on each side by several layers of vertically com- 

 pressed ones presenting a more or less columnar arrangement. 

 Central plane thinnest in the centre (where it generally com- 

 mences around one or more comparatively large " primary 

 cells " in conjunction, by which the centre, when thus exposed, 

 is easily ascertained), increasing slightly in vertical diameter 

 towards the circumference; structure of the central plane, 

 wdien viewed in a vertical section, passing through the 

 " primary cells " or centre of the fossil, presenting, for the 

 most part, quadrangular spaces. Disk of the largest specimen 

 exposed about '6^ inches in horizontal diameter by ^ inch 





