AND AYES OF NORTH AMERICA. 7-0 



HOLOPS OBSCURTJS, Leidy. 



Thoraco&aurus obscurus, Cope, Geol. Surv. N. J., App. C. C'rocodilus obscurus, Leidy, Smitbson. Contrib , 1 -0 j, 

 p. 115. Tab. II, fig. 4. Undetermined crocodile; teetb tab. I, f. 7, 8, 9. 



Tbis species was established by Prof. Leidy on vertebra? from Barnesboro, Gloucester Co. and Arneytown, Bur- 

 lington Co., New Jersey. I bave procured numerous vertebra; from the former locality, which were associated with 

 a cranium, which was nearly destroyed before reaching my hands. Enough, however, has been preserved to indicate 

 with certainty that it is agavial, and probably of the same genus as that to which Cook's Monmouth County skull 

 belonged. Numerous dermal plates were procured at the same time, which however are not more certainly to be 

 ascribed to the T. obscurus than to the T. tenebrosus, of which several portions were discovered in the same excav- 

 ations. 



The vertebra? from Barnesboro in my possession have apparently pertained to two individuals ; two cervicals, a 

 second and fifth dorsal, with six other dorsals and lumbars and a caudal, of the one, and a first and fifth dorsal with 

 eleven other dorsals and lumbar vertebra?, of the other individual. 



In addition to these, I have examined two cervicals found with muzzle and long bones at Barnesboro ; a fine 

 series of vertebra? and other bones in the Museum of the Academy from near Birmingham ; three fine series in 

 possession of Prof. G. H. Cook,f the Mount Holly Lyceum Natural History, and Prof. O. C. Marsh of Tale College, 

 all from Birmingham ; portions of two individuals in my own collection from the same place, and a set of eight verte- 

 bra? from Mullica Hill in my possession. Numerous other specimens of this species have fallen under my examination. 

 Hence it is obvious that this is the most abundant gavial of tire New Jersey Cretaceous. 



A series of cervicals from Birmingham is instructive, showing the differences in the characters of the respective 

 vertebra?, The axis, which as usual is coossified with part of the body of the atlas thereby much increasing its 

 length, has parapophyses represented by two crests directed downwards and separated by a deep longitudinal cavity; 

 they are united in front. An obtuse ridge on the side of the centrum separates two longitudinal concavities. The 

 third cervical is also deeply concave below, since the parapophyses descend much below the plane of the centrum, 

 and are united by an arched connection in front, which is not separated from the rim of the cup. As usual the para- 

 pophyses continue to rise, till on the sixth they are a little above the plane of the centrum. They also become more 

 posterior, till on the sixth their centre is opposite the middle of the centrum without ball : on the seventh this 

 point is behind the middle. The first dorsal is readily distinguished by the small size and posterior direction of the 

 articular face of this parapophysis ; its middle is a little below opposite the middle of the cup. On the third dorsal 

 the same point is just above opposite the middle of the cup. 



On the fourth cervical a trace of median inferior keel exists ; it is quite strong, but thin and concave on the fifth, 

 while on the sixth it is thicker, and does not separate deep concavities, but only slightly concave planes. It is still 

 more elevated on the seventh, and increases beyond. On the third there is no distinct hypapophysis. On the fourth, 

 a transverse elevation on the anterior arch connecting the parapophyses marks it ; on the next it appears in the same 

 place as two small longitudinal tubercles with groove between. On the sixth they are similar but stronger. Ou the 

 seventh it is much more elevated, the groove between its halves being now a transverse plane. On the first dorsal it 

 is a simple, large process, extending over half the centrum with a small knob behind it : on the third it has a longer 

 base, but on the second the longest, extending the whole length of the centrum. On the fifth it is thick, with 

 rounded edge below, and with a truncate triangular face in front. It is apparent on the eighth, as an obtuse eleva- 

 tion in front. 



From the fourth posteriorly the characters are drawn from other series, which show many of these vertebrae. 



The cups of the third to fifth cervicals look a little more truncate below, owing to the prominence of the trans- 

 verse ridge. They are almost perfectly round thence to the second dorsal, where the transverse diameter begins to 

 exceed the vertical a little. First on the fifth dorsal the cup assumes some of the narrowed form of the centrum. 



The very numerous lumbars present nothing peculiar. As in other species they are more or less striate grooved 

 at the bases of the cups and balls. 



The series first mentioned as from Barnesboro presents typical characters of the cervical hypapophyses. 



t The types of T. obscurus preserved in the museum of Rutgers College have been kindly placed in my hands by John Smock, Asst. State Geologist 



