Marsh Collection, Peabody Museum. 403 



however, is manifestly incorrect, as all the evidence from both 

 living and extinct forms tends to show. 



Their chief characters derived from the skeleton . are the 

 following : Like the preceding group, the main entocarotid 

 does not enter the tympanic chamber ; the lower incisors and 

 canines, when present, are much compressed laterally, elongate, 

 and procumbent in position ; the first lower premolar is com- 

 monly enlarged, and functions as a canine ; there is a well- 

 ossified tympanic bulla ; the fourth digit of the manus is the 

 longest of the series ; the lachrymal is very generally enlarged, 

 with extraorbital extension, and the external opening of the 

 lachrymal canal is always upon the outside of the orbit ;* the 

 lachrymal and malar are nearly always in contact. 



Just what value is to be attached to the placentation, in esti- 

 mating affinities, is a question difficult to decide, but it is 

 believed, and strongly argued by some, that the lowly organized 

 structures and generalized condition by means of which the 

 foetal envelopes develop a connection with the lining mem- 

 brane of the uterine walls during gestation furnish a sufficient 

 reason for removing the lemurs widely from the monkeys. In 

 like manner, the rudimentary condition of the posterior cornu 

 and hippocampus minor of the cerebrum, as well as the con- 

 volution of the transverse colon, have been looked upon as 

 characters of great significance in classification. While it is 

 probably true that these characters derived from the soft 

 anatomy indicate a wide distinction between existing monkeys 

 and lemurs, yet it is much to be doubted whether these dis- 

 tinctions would not assume very small proportions, or com- 

 pletely disappear, did we have an Eocene monkey with which 

 to make the comparison. 



. Touching the question of the value of the manner of placen- 

 tation as applied to the classification of the Mammalia, it is 

 well to recall the words of Flower and Lydekker on this topic. 

 In speaking of the " deciduate " and " non-deciduate " varieties 

 of placenta, they say : f "It was once thought that the distinc- 

 tion between those two forms of placentation is so important 

 as to constitute a sufficiently valid basis for a primary division 

 of the placental mammals into two groups. It has, however, 

 been shown that the distinction is one rather of degree than of 

 kind, as intermediate conditions may exist, and it is probable 

 that in different primary groups the simpler, non-deciduate 

 form may have become developed independently into one or 

 other of the more complex kinds. * * * * * We may conclude 



* An exception to this last statement is found in the extinct Malagassy lemur 

 Nesopithecus of Forsyth Major. In this species, according to its describer, 

 both the lachrymal and the lachrymal opening are within the orbit, 

 f Mammals, Living and Extinct, 1891, p. 80. 



