238 Miscellaneom. 



of reptiles, and confirms the opinion expressed in my first memoir 

 on Bicynodon, as to the " close and important relationship between 

 Dicynodon and Rhynchosaurus'^'' It similarly strengthens the 

 opinion that the formations in South Africa containing remains of 

 Dicynodon belong to the same geological system (the Triassic) as 

 the Sandstones at Grinsill, Shropshire. 



In the species of Dicynodonts already described may be seen a 

 progressive advance in the position of the pair of descending tusks 

 of the upper jaw, from below the orbits (as in D. striyiceps) to below 

 the nostrils (as in Ptychognathus declivis) ; but in Rhynchosaurus 

 the bodies which are analogous, if not homologous, take the place of 

 the premaxillary bones, and terminate the anterior contour of the 

 skull, curving down in the present as in the first-described specimen, 

 in front of the symphysis mandibulse, and presenting an exaggerated 

 condition of that pair of compound osseous and dentinal bodies 

 which hold the place of the premaxillaries in the rare existing New 

 Zealand amphiccelian lizard, Rhynchocephalusf. 



There is no trace of the deflected tusk-like bodies, in Rhyncho- 

 saurus, being implanted in bone. 



I am. Gentlemen, 



Yours truly, 



Richard Owen. 

 British Museum, Aug. 24, 1859. 



Note on Bulimus acutus. By Dr. J. E. Gray, F.R.S. &c. 



Bulimus acutus has been generally supposed to be confined, in the 

 British Islands, to the West of England and Wales : it is found in 

 abundance on the low lands on the east side of the Chesil Bank, be- 

 tween Weymouth and Portland, and also on the hills on the west of 

 Lulworth Cove. It seems to appear, in the latter place at least, 

 periodically. It is now extremely abundant, both on the grass and 

 congregated together at the roots of the sea-beet, near the coast- 

 guard signal station ; but the coast-guardsman, who has been on the 

 station several years, said he had not seen it before this year, and he 

 believed that they had been blown from the opposite hills ! perhaps 

 he only meant to say, in such abundance. Now it is even more 

 common than Helix virgata, with which it is found. 



Swanage, August 1859. 



Note on the Opercula of several Species of Megalomastoma. 

 By W. H. Benson, Esq. 



The structure of the horny operculum of Megalomastoma cylin- 

 draceuMy Ch., approaches, at its dorsal side, to that of Hybocystis, 

 differing from the numerous spiral volutions visible on that part of 

 the thin horny operculum of the Himalayan M. funiculatuMj and 



* Trans. Geol. Soc, 2nd ser. vol. vii. p. 67 (1845). 

 t Ibid., vol. vii. pi. 6. fig. 519. 



