62 MOSASAURUS. 



tooth last described. .The crown Avhen perfect has measured less than three-fourths 

 of an inch in length, is elliptical in transverse section, and measures at base five 

 lines and three-quarters antero-posteriorly, and four lines and a half trans\ersely. 

 Its single posterior carinated ridge is minutely denticulated as in the large teeth, and 

 the surfaces are devoid of planes. 



The fang, independent of the alveolar fragment Avith which it is coossified, 

 measures about an inch and a half long, and has at its inner side posteriorly a deep 

 excavation for a successional tooth, as seen in Fig. 5, a. 



15. A perfect tooth, coossified with a fragment of the jaw, from Monmouth 

 County, New Jersey, loaned by William Cornell, through Prof. Cook. The speci- 

 men Avas received after the present memoir and its accompanying plates were 

 nearly completed. It closely resembles the eighth specimen of the series above 

 described. The crown is unworn, is twenty lines long, and is elliptical in transverse 

 section. Its base is one inch in diameter antero-posteriorly, and nine lines and a 

 half transversely. It possesses a single ridge, situated along its posterior or concave 

 border ; and the surfaces are smooth, except that the outer one presents a feeble 

 disposition to subdivision into four planes. The lower of the accompanying outlines. 

 No. 17, represents a section from near the base. The fang is three inches long. 



16. Two teeth, from Monmouth County, New Jersey, presented to the Academy 

 of Natural Sciences by Dr. J. H. Slack. One of the specimens resembles the two 

 large ones last described. The crown has the apex broken off, but is otherwise 

 perfect. Its transverse section is elliptical, and measures at base antero-posteriorly 

 thirteen lines; transversely ten lines and a half. It possesses a single carina, 

 situated posteriorly, and the surfaces are totally devoid of planes. The accompa- 

 nying right hand outline, Avith one point, No. 18, represents a section near the base. 

 The fang is about three inches long, and exhibits on its inner sidf; near the centre 

 a slight excavation, five lines long, as the commencement of a cavity for a successor. 



The canal communicating Avith the pulp cavity through the 



Nn. IS. r ■ 



tang IS open. 



The second specimen, represented in Fig. 7, Plate IX, is 

 nearly perfect, and measures about four inches and a half long. 

 It corresponds in all its anatomical characters Avith the teeth 

 described by Prof. Owen as characteristic of a distinct genus, 

 to which he has giA'en the name of Leiodon. 

 The croAvn is tAvcnty-one lines long, elliptical in transverse section, as represented 

 in the accompanying left hand outline, Avith tAvo points. No. 1 8, and measures at 

 base antero-posteriorly thirteen lines ; transversely eleven lines. Minutely denticu- 

 lated ridges divide it in the usual manner into inner and outer surfaces of nearly 

 equal extent and convexity and totally destitute of subdivisional planes. 



The fang is straight, and presents no trace of having been coossified Avith its 

 alveolus, as is also the case with that of the preceding specimen. It further exhibits 

 no trace of a caA'ity for a successional tooth. 



17. The shed croAvn of a tooth, from St. Georges, Nbav Castle County, DelaAvare 

 contained in the museum of the Academy of Natural Sciences. It is represented 

 in Fig. 11, Plate IX, and resembles the corresponding part of the tooth just 



