Notices of Memoirs — M. Broivn — On Colobodus. 501 



Although there are in the district many northern erratics, notably 

 a large boulder of granite and another of picrite, which the author 

 found on Porthlisky farm, two miles south-west of St. David's. 3'^et 

 by far the majority are of local origin, and can be traced back to 

 the parent rocks. The great igneous masses which now form such 

 conspicuous hills along the north coast yielded most of the boulders, 

 many of very large size, which are so freely spread over the 

 undulating land reaching to the coast of St. Bride's Bay. There are 

 clear evidences to show that this bay was itself overspread by a 

 great thickness of drift from these hills. Tbe intervening pre- 

 glacial valleys were also filled by this drift, and the plains and. 

 rising grounds up to heights of between 300 and 400 feet still 

 retain evidences of its former presence, and many perched blocks. 

 Excellent sections of unstratified drift, containing large ice-scratched 

 boulders, are exposed in Whitesand Bay, and a thickness of several 

 feet of an irregularly stratified sand was, some time since, exposed 

 under the Boulder-clay on the east side of the bay. Chalk flints 

 have been found at heights of over 300 feet, having probably been 

 brought from Ireland. The picrite boulder already referred to has 

 been shown by Prof. Bonney to resemble masses of that rock 

 exposed in Carnarvonshire and Anglesea, and the granite boulder, 

 which before it was broken must have been over 7 feet in length 

 and 3 to 4 feet in thickness, is identical with a porphyritic granite 

 exposed in Anglesea, but not found anywhere in Pembrokeshire. 

 The evidences, therefore, which go to prove that Pembrokeshire 

 was buried under an ice-sheet that must have spread southwards 

 into the Bristol Channel, are, the presence of many northern 

 erratics, both as perched blocks and in drifts at heights above 

 300 feet, ice-scratched, smoothed and polished rock surfaces, and, in 

 places, much crushing and bending of some of the strata; also great 

 dispersions of boulders from igneous rocks on the north coast in 

 a south-west direction, and some well-marked examples of ' crag 

 and tail.' 



IV. — Notes upon Colobodus, a Genus of Mesozoio Fossil Fishes. 

 By Montagu Browne, F.Z.S., F.G.S. 



COLOBODUS appears to have been first constituted a genus in 

 the year 1837 by Louis Agassiz (see ' Poissons Fossiles,' 

 Tome II., ii^ partie, p. 237), who gave this name to some Lepidotus- 

 like teeth (Colobodus hogardi) from the Muschelkalk, which he 

 described thus : — " Par leur taille elles tiennent le milieu entre les 

 Microdon et les Sphserodus. De formes arrondies et cylindracees 

 vers la base, les dents ont leur couronne renflee en forme de massue, 

 et sur le milieu de la couronne s'eleve encore un petit mammelon 

 tronque, ce qui a valu a ce genre son nom de Colobodus." 



Since that time teeth of a similar generic character have been 

 described or figured by various authors, e.g., Count Miinster 

 (assuming Asterodon to be identical), Plieninger, Giebel, Gervais, 

 Meyer, Chop, E. E. Schmid, Alberti, Eck, Winkler, Giirich, W. 

 Dames, and A. S. Woodward. The typical teeth, however — i.e. those 



