io6 STUDIES IN GEOLOGY, No. i 



pods. Lonchocarpus with many small shrubby species 

 inhabiting xerophytic regions invites comparison as a type 

 likely to occur in such an association as that represented 

 by the Corocoro flora. On the other hand its existing 

 distribution is on the whole nearer the equator than Dal- 

 bergia in South America. Both genera have been described 

 from Potosi on the basis of leaflets, but unfortunately 

 little reliance can be placed upon these determinations, 

 since the most that can be expected is the recording of 

 resemblances to recent forms and these can be considered 

 conclusive only when they present distinctive features not 

 shared by numerous other genera of the Leguminosse. 



In referring to Engelhardt's species in 1918 I questioned 

 (i) the generic reference commenting that this pod was 

 more likely to be a Cassia, since no traces of seeds were 

 seen. In the light of the material which I collected at 

 Corocoro it is seen that there is no close similarity to 

 Cassia. The single specimen upon which this species rested 

 was contained in the collection of the Royal Silver Mine 

 of Potosi Co., in London and the tip was broken away and 

 restored in Engelhardt's figure. The present material 

 shows that it was obtusely rounded and not acute as 

 restored. . The type specimen does, however, show the 

 stipitate nature of these pods all of the Corocoro material 

 being broken from the calyx. I have no doubt, however, 

 of the identity of the two occurrences, thus adding to the 

 Corocoro flora another element found at Potosi. 



Although positive generic determination is not possible 

 I am sure that the fossil belongs to the tribe of Dalbergiese 

 and therefore the genus Dalbergia may stand in a broad 

 sense as indicative of the true botanical affinity of the 

 fossil and in this connection it is pertinent to call attention 

 to the stereotyped paleobotanical practice of referring 

 fossils to the genus Dalbergia in many cases where it is 

 the tribe rather than the genus that is determinable. 



1 Berry, E. W., Proc. U. S. Natl. Mus., vol. 54, p. 149, 1918. 



