MiKSH.] PLEUROCCELID.E. 1 83 



projects forward and downward, uniting with its fellow on the median 

 line in a strong ventral symphysis. Its upper posterior margin meets 

 the ischium and contains a large foramen. The ischium projects down- 

 ward and backward, and its distal end is not expanded. The relative 

 position and general form of the three pelvic bones in this genus are 

 shown in PL XXXVI, fig. 1, and the entire pelvic arch in PL XXXI. 

 The ischia of two species are shown on PL XXXY. The sacrum of one 

 species of Morosaurus is shown on PL XXXI, and that of another on 

 PL XXXIII. A cast of the sacral cavity of the latter is represented in 

 fig. 34, p. 182. 



THE HIND LIMBS. 



The femur is long and massive, and without a true third trochanter, 

 although a rugosity marks its position. The great trochanter is obtuse 

 and is placed below the head. The ridge which plays between the tibia 

 and fibula is distinct. The tibia is shorter than the femur. It is with- 

 out a spine or fibular ridge, and its distal end shows that the astrag- 

 alus was separated from it by a cushion of cartilage. The fibula is 

 stout, its two extremities nearly equal, and its distal end supports the 

 calcaneum. The tarsal elements of the second row are unossified. The 

 five well-developed digits are similar to those in the maims. The first 

 metatarsal is much the largest (PL XXIX, fig. 2). The feet are also 

 shown on Pis. X XX VII and XXXVIII. 



PLEUROCCELIDJE. 



PLETJROCCELUS. 1 



THE SKULL. 



The genus Pleurocoelus includes the smallest individuals of the 

 Sauropoda found in this country, most of them not being larger than 

 existing crocodiles, and some even smaller. The skull is quite small? 

 and resembles in its structure that of Morosauras, but has points of 

 similarity also with that of Brontosaurus. The teeth resemble those of 

 Diplodocus most nearly, but have shorter roots and are much more 

 numerous, the entire upper and lower jaws being furnished with teeth. 

 The dentary bone is similar in shape and proportions to that of Bron- 

 tosaurus, differing widely from that of Diplodocus and Morosaurus. 

 It is slender and rounded at the symphysis, instead of having the mas- 

 sive, deep extremity seen in Morosaurus. The maxillary also is much 

 less robust. The supraoccipital agrees closely in shape with that of 

 Morosaurus, and forms the upper border of the foramen magnum, as 

 in that genus. In PL XL, fig. 1, is shown the dentary of Pleurocoelus, 

 with the teeth in outline, and beside it are typical examples of the teeth. 



THE VERTEBP.iE. 



The cervical vertebra? are very elongate and strongly opisthoccelous. 

 The deep cavities in the sides of the centrum are separated only by a 

 thin septum of bone, as shown in fig. 3 of the same plate. The dorsal 



1 American Journal of Science, 1888. 



