334 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 



between the first and the margin; from tlicse 

 three arise several others of equal strength, 

 there being altogether 10 or 12, close, parallel, 

 and all curving around to and apparently 

 entering the tip; no other nervation discernible. 



This curious little leaf is absolutely perfect 

 except a minute portion of the tip. It is about 

 22 mUlimeters long includmg the narrow basal 

 portion or petiole, which is 3 millimeters in 

 length and 15 miUimeters wide. It is almost 

 elliptical, though it is perhaps 1 miUimeter 

 broader in the lower portion than in the upper. 

 There are 11 or 12 nerves, only three of which 

 arise in the basal portion, the others arising 

 from them and aU running into the tip. 



The genus Heteranthera is a small one, 

 comprising about nine species, two of which 

 occur in tropical Africa and the others in 

 America. Only three species are found ui the 

 United States. They are herbs growing in mud 

 or shallow water, with creepmg, ascending, or 

 floating stems and petioled leaves which may 

 be cordate, ovate, oval, reniform, or even 

 grasslike. Of the tlu'ee United States species 

 the one most smiQar to the present form is 

 Heteranthera limosa (Swartz) WUldenow, the 

 smaller mud plantain, which ranges from Vir- 

 gmia to Kentucky and Missouri, south to 

 Florida and Louisiana, and thence throughout 

 tropical America. The living species bears 

 numerous oval or ovate leaves 1.5 to 2.5 centi- 

 meters long on petioles 5 to 12 centmieters 

 long. The several nerves all arise from or near 

 the top of the petiole and arch around to 

 the tip. 



It win be noted that the fossil fonn agrees 

 closely with this livhig species, the leaf bemg 

 more nearly elliptical or ovate-eUiptical and 

 more abruptly pointed at the apex. The 

 nerves as they pass from base to apex are very 

 similar in both forms, but m the fossil leaf they 

 do not all arise from the top of the petiole, as 

 apparently they do in the living species. It is 

 believed that the generic reference can hardly 

 be cjuestioned. 



This species undoubtedly resembles and 

 indeed may be identical with a little leaf from 

 Point of Rocks, Wyo., which was referred by 

 Lesquereux * to Lemna scutata Dawson and 

 which I afterward,- probably incorrectly, re- 



1 Lesquereux, Leo, U. S. GeoL Sun-ey Terr. Rept., vol. 7, p. 102, pi. 

 6L flg. 5 [not flg. 31, 1878. 



2 Knowlton, F. H., U, S. Geol. Survey Bull. Iii3, p. 31, 1900. 



garded as merely a small leaf of Pistia corrugata 

 Lesquereux. The leaf from Point of Eocks is 

 much smaller thiin the leaf here described and 

 is more nearly circidar, but the "petiole" and 

 the disposition of the nerves is much the same 

 m both. It is certainly clear that the present 

 leaf, as wcU as the one from Pomt of Rocks, is 

 not the same as the type specimens of Dawson's 

 Lemna scutata, and it is also reasonably certain 

 that the present leaf can not belong to the 

 genus Lemna. 



Occurrence: Fruitland formation, Coal 

 Creek, 35 mUes south of Farmington and 1 mQe 

 east of reservation line, San Juan County, 

 N.Mex. Lot 8 1(6955). 



Family ARACE.ffi. 

 Pistia corrugata Lesquereux. 



Plale LXXXV, fi,5ure 4. 



Pistia corrugata Lesquereux, V. S. Geol. and Geog. Survey 



Terr. Ann. Rept. for 1874, p. 299 [1876]; U. S. Geoi. 



Survey Terr. Rept., vol. 7, p. 103, pi. (51, fig?. 1. 3, 



4, 6, 7, 9-11, 187S. 



Knowlton, U. S. Geol. Survey BulL 103, p. 31, 1900. 



One of the collections from the San Juan 

 Basin contains a single example with its coun- 

 terpart that undoubtedly belongs to Pistia cor- 

 rugata as described by Lesciuereux from speci- 

 mens collected in the Montana group at Pomt 

 of Rocks, Wyo. As may be seen from the fig- 

 ure, it is considerably broken and adds httle 

 or nothing to our knowledge of the species. It 

 is about the same as the specimen shown in 

 figure 7 of Lescjuereux's plate in volume 7 of 

 the Hayden Survey reports, in that it appears 

 to be attached to the side of the thick stem, 

 though it is perhaps really terminal and has 

 been distorted in position dm-uig entombment. 

 There appears to be a mass of rootlets by the 

 side of the base, but these are so matted and 

 compressed that their character can not be 

 made out. The nervation is the same as that 

 figured by Lesc^uereux, namely, an mdetermi- 

 nate number of veins arising in the base of the 

 bliide and spreading out and variously anasto- 

 mosing above, producing very irregular polyg- 

 onal meshes. 



Pistia corrugata is said to be very abundant 

 at Point of Rocks, Wyo., Lesquereux describ- 

 ing it as "covering by itself only large surfaces 

 of shale." It was also found bi beds of similar 

 age at Superior, Wyo., by Schultz in 1907, hi 

 beds believed to be of Mesaverde age m the 



