AND AVES OF NORTH AMERICA. 



193 



trernity an open sigmoid, characters which might be included in the range of variation of the M. dekayi. The form 

 of the oauda] vertebrae is that of M. maximus, and differs from that of M. dekayi. The characters by which the os 

 quadratnm differs from that of M. maximus, are, as Prof. Marsh informs me by letter, the great development of the 

 meatal knob, and the slight prominence of the median posterior ridge, which is a strong process in M. maximus. 

 These characters are marked, but their value may not be as yet fully established. The great ala is plane, and with a 

 deep marginal groove. 



The number of mandibular teeth (17) distinguish it from M. giganteus. Their crowns arc divided into the two 

 usual planes, and arc scarcely facetted. They are more than usually curved outwards in the specimen described. 



The cups of the vertebra are nearly round or slightly depressed. Measurements sent by Prof. Marsh are as follows: 



Median dorsal, length, 

 Diameter oup, transverse, 



" " vertical, 

 Median caudal, length, 

 Diameter cup, transverse, 

 " " vertical. 



Chevron bones ooossifled. 



Lower marl bed of the upper cretaceous at Hornerstown, Monmouth Co., N. .T. Established on a nearly perfect 

 cranium, five feet in length, and numerous vertebra. Discovered by Jno. Q. Miers. 



n. 



Lin. 



4 





8 





3 



4 



2 



8 



8 



3.5 



2 



10.7 



MOSASATJ.IUTS DEKAYI, Bronn. 



Letheea Geognostica 1838; e Dekay Moaaaaurua in Annals Now York Lye. Ill, 135 

 Tab. Mosasaurua major, Dekay, Palaeontology Now York Geolog. Survey, 1841. ?Mo- 

 sasaurus carolinensis, Gibbes, Smithson. Contrib. to Knowl. II, tab. M. couperi, Gibbes, 

 l.o. Mosasaurua mitchillii, Leidy, Proceed. Acad. Nat. Sci., Phila., 1856; Smithson. 

 Contrib. p. IIS, tab. nee Oeosaurua mitchillii, Dekay Liodon mitchilliihujus operis. 

 fBaaeodon reveraua, Leidy, Cretac. Reptiles, p. 118, Tab. X, 14-15. 



This species is most abundantly found in I he upper oretaceous green sand of New Jersey. Portions of many in- 

 dividuals have passed under my observation; among them two presented quadrate bones, and several the separated 

 elements of the atlas. The same pieces, id' several other species, arc fortunately at my disposal, and the preceding 

 cuts present the speciflo characters to be observed in them, very dearly. 



Of a specimen of this species from Holmdel, Monmouth Co., N. .1.. described by Leidy, there is sufficient material 

 to determine the relative proportions of many parts of the cranium. The muzzle is figured in his Tab. XIX fv. (! 

 and shows the distinct elevation of the premaxillary bone. This portion is lost in the M. giganteus. Both the quad- 

 rate bones and the teeth are rather smaller than in the M. giganteus of Maastricht, but numerous isolated teeth 

 occur, which are identical in form with those <>[' the present specimen, which indicate a, size fully equal. The neura 

 pophysial pieces of the aliases of the two, when compared, (see Ossemens Fossiles) present marked differences. 



A lew lumbar vertebra- have, been figured by Leidy. In my private collection arc shorter or longer scries from 

 the columns of four additional individuals. Three are from the long lumbo-sacral region; one consists of eleven ver- 

 tebra; their length together is 20 in. 10 lines. A series of live median caudals measures 7 in. 10 [in. 



In the Museum <>l' the Academy Natural Sciences, are portions of the vertebral columns of six individuals, but none 



of them include dorsals, and they differ very much in size. They are all pentagonal rounded at the extremities, more 

 elevated and angular than in M. maximus. The caudals belong to the larger series and have well developed diapo- 

 physes and anchylosed chevron bones. The caudals in my private collection are smaller, also pentagonaj ami with 

 chevron bone articulated to slightly elevated bases, The caudal vertebra on which Morton founded his M. occiden- 



A.MEEICA. PHILO. 800. — VOL. XIV. 49 



