GROUND SLOTHS IN THE CALIFORNIA QUATERNARY 613 



only possible source of such a specimen as that which we have under considera- 

 tion is the more recent deposit. 



Incoherent, yellowish, sandy clays, similar to those just mentioned, form the most 

 prominent feature of the geology along the east side of Tomales bay between Point 

 Reyes station and Hamlet. In many places they form prominent seacliffs up to 

 40 feet in height. They are everywhere unsolidified and frequently show hori- 

 zontal stratification. Mr Calkins considers the beds in the stream cutting in 

 which the humerus was found as an extension of this deposit up the slope of the 

 hill. Judging from their incoherent nature and horizontal stratification, these 

 beds are certainly much younger than the latest Pliocene in the region. Except- 

 ing the humerus, the only fossil obtained from them is a badly worn elephas tooth, 

 which was picked up on the shore of Tomales bay near Point Reyes. This forma- 

 tion resembles the deposits along the shores of San Pablo and Suisun bays, in 

 which a Quaternary fauna, both molluscan and mammalian, has been obtained 

 by the writer. In this connection the preservation of the specimen is a note- 

 worthy character, as the bone is absolutely intact and the original material 

 unchanged. One might almost suppose it a product of the last half century. 



Two edentate humeri, much resembling the specimen under consideration, 

 have been described from western North America. The first specimen was dis- 

 covered on the Willamette river, Oregon, in 1839, by Mr Ewing Young. In 1842 

 it was described and figured by H. C. Perkins.* The humerus and a large gravi- 

 grade tooth, associated with elephas and bos or bison remains, were found about 

 12 feet below the surface, presumably in a Quaternary deposit. This specimen was 

 provisionally named Orycterotherium oregonensis, but was afterward referred to 

 Alylodon by Sir Richard Owen. 



The other specimen, together with a femur, was obtained by Marsh from Alameda 

 county, California (locality unknown), and was described by him as the type of 

 a new genus, Morotherium, species gigas. Marsh considered Morotherium most 

 nearly related to Megalonyx and Mylodon, being distinguished from the former by 

 the absence of a supra-condylar foramen in the humerus, and from the latter by the 

 absence of a depression for the round ligament in the head of the femur. 



Unfortunately in the type specimen of Morotherium gigas the only portion of 

 the humerus preserved is the distal end, minus the outer and inner condyles, so 

 that it is not possible to make a satisfactory comparison. To as much of it as. is 

 preserved, the Tomales Bay specimen shows a strong resemblance. With the 

 Willamette River humerus, of which good outline drawings were given by Perkins, 

 our specimen agrees perfectly, excepting in one particular. In Perkins' drawings 

 the deltoid ridge shows a deep narrow notch near the lower end, which is not pres- 

 ent in the Tomales Bay specimen. In his article Perkins states that there are 

 remains of a large protuberance on the outside of the humerus, a little more than 

 half way down the body of the bone, so that the notch in the deltoid ridge is 

 possibly an irregularity in the weathered or broken bone. In the figures of the 

 humerus of Mylodon which the writer has seen no such notch appears. The two 

 specimens are of nearly the same dimensions throughout. The principal differ- 

 ence is in the length, the Willamette specimen measuring about 20, the other 18 J 

 inches long. The humerus of Morotherium gigas is about the same size as the 

 other two specimens. 



*Amer. Jour. Sci., vol. 42, p. 137. 



