Morris — On Sarsen-stones. '^3 



The first and second of the teeth meet above the symphysis, as in 

 CocJiIiodus ; the third pair are rather wider apart than in that genus. 

 The angle at which the two rami meet at the symphysis, is inter- 

 mediate between those that respectively characterise the mandibles 

 of CocJiliodus and Streblodus. 



The first tooth (Fig. 2, a) of Tomodns is relatively smaller to the 

 the others than in CocMiodus ; it is also more simple and conical in 

 form — so far it resembles more the anterior teeth in Cestracion, but the 

 apex is obtusely rounded. The second tooth has similar proportions 

 to those in Cochliodiis, but the middle lobe is somewhat less convex, 

 and a posterior seam is better indicated. The third tooth (Fig. 2 c) 

 is longer from before backward, in proportion to its breadth, than in 

 CocMiodus, and it differs both from it and from Streblodus, in the 

 lower and more general convexity of the grinding surface of the 

 last tooth. This surface has been crushed in the specimen here 

 figured, but will be illustrated, as also the teeth of Streblodus, from 

 better preserved detached specimens, in a consecutive paper. 



EXPLANATION OF PLATES III. & IV. 

 PLATE III. 

 Fig. L Upper view of dentary part of the mandible, and of the teeth of Cochlioduit 

 contortus, Ag. From the Mountain Limestone of Bristol. Wood- 

 wardian Museum. 



2. Outside view of right ramus of ditto ; a. surface from which the right 



anterior tooth has been detached ; a', corresponding tooth of left ramus ; 

 b. right middle tooth ; b'. part of left ditto ; c. right posterior tooth, outer 

 margin of. 



3. Posterior view of part of mandible and teeth of Streblodus ohlongus, Ag. 



From the Mountain-Limestone of Armagh. Museum of the Earl of Ennis- 

 killen. 



4. Right third tooth of CocMiodus contortus, Ag. 



5. Left third tooth of Cochliodus contortus. Both this and Fig. 4 are from the 



Carboniferous Limestone, Bristol. Museum of the Earl of Enniskillen. 



PLATE 17. 



Fig. 1. Right third tooth of Cochliodus compaclus. From Carboniferous Limestone 

 of Yorkshire. "Woodwardian Museum, Cambridge. 



2. Upper view of mandible and teeth, Tomodus convexua, Ag. 



3. Under view of ditto. 



4. Outer side of right ramus of ditto. 



5. Inner side of ditto. From the Carboniferous Limestone, Bristol. Museum 



of the Earl of Enniskillen. 



III. — On the Occurrence of Gtret-Wethers at Grays, Essex. 

 By Professor John Morris, F.G.S. 



THE occurrence of "Sarsen-stones," or blocks of so-called Druid 

 sandstone, has not, I believe, been generally noticed in this locality, 

 and their position may be of interest to some of your readers, more 

 especially as the extensive workings both for Brick-earth and Chalk 

 have obliterated many of the interesting sections for which the pits 

 were celebrated.' Grays is well known both for its fine chalk-pits 

 and extensive brick-earth deposits, the latter containing numerous 



1 Mag. Nat. Hist. 1836, p. 261 ; 1838, p. 539. 



