1867.] BOYD DA^^KIXS EHIXOCEROS LEPTOEHTS-US. 221 



the left side, with the exception of premolar 2. With the following 

 exceptions they present all the characteristics of the series obtained 

 from Lexden, above described. Premolar 3 presents a faint cusp at 

 the entrance of the anterior valley (a) close to the cinguliim. Pre- 

 molar 4 has the posterior corahing- plate (h) divided into three 

 secondary folds, as in a corresponding tooth of the megarhine 

 species, fi:om the Forest-bed of Cromer, preserved in the collection of 

 the Rev. J. Gunn, F.G.S. The first upper true molar also has a 

 small cusp at the entrance of the anterior valley, and has the third 

 collis divided from the second by a shallow notch, which, being worn 

 away at an early period in the life of the adult, is not very often seen 

 in the upper molars. 



In the river- deposits of the Thames valley a leptorhine premolar 

 4 and molar 2 (fig. 5) were discovered in 1862, during the main- 

 drainage works near Peckham, on the Surrey side of the Thames, and 

 deposited in the British ]\Iuseum. The matrix proves them to have 

 been derived from a pale-grey clay, a point which is of considerable 

 importance as marldng the relative age of the leptorhine and ticho- 

 rhine species in that particular locality. The premolar is remarkable 

 for the development of two accessory corahing -plates from the median 

 collis, and their fusion, so that two accessory valleys are mapped off. 

 The crown is uneven, and the tliird costa (h 3) strongly marked. 

 The tTiird collis is notched and cuspless. The true molar differs from 

 the ordinary type of leptorhine upper molars, and approximates to 

 the megarhine, in the external lamina not being hoUowed basally ; 

 and were it not for the unequivocal evidence of the premolar 4 that 

 belonged to the same jaw, it would be altogether a doubtful tooth. 

 The Lower Brick-earths of Gray's Thurrock in Essex have furnished 

 a second instance of leptorhine remains being found in the valley of 

 the Thames, in a first upper true molar that agrees in all essential 

 points with that from Clacton, figured by Professor Owen (Foss. Mam. 

 fig. 141). The most remarkable discovery, however, is that made 

 by Mr. Antonio Brady, F.G.S., of a leptorhine skull and lower jaw 

 at nford. The former is very nearly perfect, and exhibits the 

 demi-cloison or partially ossified septum between the nares, and the 

 entire upper molar series. It also satisfactorily settles the question 

 of the upper dental formula, as no trace of the premolar 1 is to be 

 found on either side. TVith the exception of the last upper true 

 molar, the description of the teeth from Lexden applies to these also, 

 the tJiircl collis in the leptorhine (M 3) taking the form of a small 

 cusp on the posterior border of the tooth, while in this it takes the 

 form of a ridge. This variation is found also in the coresponding 

 molars of R. tichorliinns. A fragment of the skull of the leptorhine 

 species obtained from the same locahty, in the cabinet of Dr. Cotton, 

 F.G.S., exhibits also the entire upper molar dentition. With the 

 exception of premolar 2, the first of the series, all the teeth bear the 

 third costa {Jc 3) faintly developed. Leptorhine upper molars have 

 been yielded also by the brick-earth on the south side of the Thames, 

 at Crayford in Kent, and are in the collections of Dr. Spurrill and 

 Mr. Grantham, to whose courtesy I am indebted for their examina- 



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