Decembee 6, 1912] 



SCIENCE 



801 



the worm has been seen to pass through two 

 complete cycles of development. In one sub- 

 culture the worms have multiplied and re- 

 mained actively viable for 23 days, without 

 transplantation. 



A striking peculiarity of the growth on the 

 agar cultures is the tendency of the worms to 

 crawl up on the side of the test-tube opposite 

 the slant and there clump themselves into 

 macroscopic groups. Under the low power, 

 ^ these groups are seen to consist of an immense 

 number of very actively motile nematodes in 

 all stages of development. 



As yet, we have not determined the exact 

 species of this nematode, but in all probability 

 it belongs to the AnguillulidsB. 



N. B. — Since the above was written we have 

 learned from Professor Henry B. Ward of 

 similar cultivation experiments carried out in 

 his laboratory by H. Metcalf.' 



Wade W. Oliver 



recently proposed species of the genus 

 diceratherium 



Since the opening of the Agate Spring 

 fossil quarries in the Miocene formation of 

 Sioux County, Nebraska, by the Carnegie Mu- 

 , seum field parties some eight or nine years 

 ago, there has been great activity by many in- 

 stitutions and private parties in this general 

 field. As a consequence much material of 

 fossil remains has been gathered, of which the 

 greater portion, especially in the Agate Spring 

 fossil quarries, consists of bones pertaining 

 to the Ehinocerotidss. 



Pending the publication of a more extended 

 work on the American Diceratheres, now in 

 progress, the purpose of this note is to avoid 

 the recurrence of certain interpretations on 

 the part of students interested in the question 

 of deciduous and permanent teeth. 



In recent years there have been a number 

 of new species described of Professor Marsh's 

 genus Diceratherium which will be duly con- 

 sidered later. In 1908 Professor Loomis, of 



'"Cultural Studies of a Nematode Associated 

 with Plant Decay, ' ' Trans. Amer. Mioroscop. Soc, 

 1903, 24, p. 89. 



Amherst, proposed a number of new forms.* 

 One of these (D. aberrans, p. 59) is established 

 on a second deciduous cheek-tooth of the left 

 side. Very recently Mr. Harold J. Cook has 

 unfortunately used deciduous teeth as a type 

 of still an additional species D. loomisi.' The 

 type of this latest species consists of a por- 

 tion of the right upper maxilla, containing not 

 P*, M^ and M^ as Cook states, but the second, 

 the third and the fourth deciduous cheek-teeth. 

 This is abundantly demonstrated in the large 

 collection from the Agate Spring fossil quar- 

 ries now under study in the Carnegie Museum. 

 In this connection it is well to state that the 

 formation of the permanent premolars 2, 3, 4 

 of Diceratherium starts comparatively late. 

 I have excavated maxillae (Nos. 2464, 2476, 

 Carnegie Museum) of young specimens and 

 often find that while the deciduous 2, 3 and 4 

 are considerably worn the germ of P', which 

 is located immediately above the roots of If, 

 is only very slightly and more often not at all 

 indicated. At the same time PS which is 

 erupted in an early stage, is on an even grind- 

 ing plane with the milk teeth and has received 

 considerable wear; more than half of the 

 grinding surface of M' appears through the 

 alveolar border, while W is represented by a 

 large excavation immediately back of M^. In 

 comparing Mr. Cook's figures {I. c, p. 31) I 

 judge that he has described a young specimen 

 of D. coohi in the stage of development de- 

 scribed above. In a later stage of develop- 

 ment (specimen No. 1848) the formation of 

 the permanent premolars is well advanced, es- 

 pecially in 2 and 3. M' is completely erupted, 

 M" appears in a large triangular opening of 

 the alveolar border, while M^ is represented 

 by a similar excavation to that of Nos. 2464 

 and 2476 above described. Thus it is repeat- 

 edly demonstrated that a large collection of a 

 genus or species is extremely useful as a safe- 

 guard against the misinterpretations of which 

 the systematists are surrounded. 



O. A. Peterson 



^ American Journal of Science, Vol. XXVI., pp. 

 51-64, 1908. 



' Nebraska Geological Survey, Vol. VII., Part 4, 

 pp. 29-32. 



