KNowLTON.] BIOLOGHCAL CONSIDERATIONS. 99 



whereas they are entire in the latter. Assuming that the evolutional 

 tendency is to get rid of these large stipular organs, as suggested in 

 the living P. occidentalism the Bridge Creek form would represent a 

 more recent and highly developed stage than P. hasilohata^ a supposi- 

 tion borne out by the relative ages of the beds in which they are found. 



Another interesting form, unfortunately represented by only a sin- 

 gle example, was identified by Lesquereux as P. nolnlis? Newb. It 

 is a leaf more than 25 cm. long and 23 cm. broad, with a petiole 8 cm. 

 long and some 7 mm. in thickness. The margin is not well preserved. 

 This may well be the P. noh'dls of Newberry, but additional material 

 will be necessary to definitely establish the fact. The well-known P. 

 aceroides of Europe and this country was also determined by Lesque- 

 reux from the Mascall beds, but it rests on two examples, neither of 

 which agrees entirely with the ordinary figures of this species. Addi- 

 tional material is needed to settle the status of this species also. 



The Rosace* are represented by two species of Cratsegus and two 

 of Prunus, one of the latter being more or less open to question. 

 Cratcegm jlavescens Newberry, from Bridge Creek, is a well-marked 

 species. It is undoubtedly similar to what was called C. Jlava Ait., 

 but which has now been segregated into several closely allied forms. 

 Lesquereux's Myrica diversifolia is clearly the same as O. jlavescens 

 and has been united with it. A form quite similar to Jlavescens^ but 

 undoubtedly distinct, I have called C. hnparllis. It is a small seven- 

 lobed leaf. 



The form that I have named Prumisf Merriami is a small ovate leaf 

 with finely serrate margins, and in appearance quite like some forms 

 of the living P. virginiana, P. demissa^ etc. It also resembles some 

 species of Cydonia, as C. japonica. 



Closely related to I\ Merriami^ and possibly identical with it, is 

 what I have called P. txifacea. It is from the same beds, but differs in 

 a number of minor particulars, being elliptical or slightly elliptical- 

 obovate instead of ovate, and has finer, more regular, and evidently 

 sharper-pointed teeth. 



The family MimosacesB is represented by a single pod, which was 

 named Acacia oregoniana by Lesquereux, 



The presence of the Ceesalpinaceaj in this ilora is open to doubt, as 

 it depends solely on the problematical form referred to Cassia by New- 

 berry. Judging from the drawing alone, it would be concluded at 

 once that it represented a small pod, but a careful study of the tj^De 

 specimen shows that this is not a fair interpretation. It may be a 

 small pod, but this is extremely doubtful, and even granting this, the 

 reference of it to Cassia is open to the gravest question. 



The presence of the Simarubaceffi rests on what Les([uereux has 

 identified as a species of Ailanthus. This consists of a branch and a 

 number of samaras, all preserved in the same piece of matrix. In the 

 first place, they have not been correctly described and figured by 



