GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 13 



Plate 7. 



Fig. 1. Lithothamnium vaughanii M. A. Howe. Photograph of the type- 

 speciinens (between Monte Lirio and Bohio Pudge. MacDonald and 

 Yaughan, Cat. No. 35290. U.S.N.M.), natural size. 



2. Lithothamnium vaughanii. A section showing irregular zonation, tetra- 



sporic conceptacles. etc., enlarged 42 diameters. 



3. Lithothamnium isthmi M. A. Howe. A section, slightly enlarged (11/8 



of the natural dimensions), showing the type-specimen embedded in 

 the matrix (from about 4 miles north of Gamboa Bridge, MacDonald 

 and Yaughan, station 6021). The type material (Cat. No. 35301. 

 U.S.N.M.), from which the section shown in plate 9 was obtained, 

 occupies the central portion (if the light area and is overgrown by 

 crusts of what appears to be a different plant, probably a species of 

 Lithophyllum. 



Plate 8. 



LithotJiamnium vaughanii M. A. Howe. 



An enlargement of a part of the section shown in figure 2. plate 7, illus- 

 trating form of perithallic cells, the reduced secondary hypothallia, the some- 

 what specialized roof of the tetrasporic conceptacles. etc. Magnification 100 

 diameters. 



Plate 9. 



Lithothamnium isthmi M. A. Howe. 



A section of the type material (MacDonald and Yaughan, station 6021, Cat. 

 No. 35301, U.S.N.M.), enlarged 100 diameters. The section shows the well- 

 developed " coaxial ' : hypothallium, the smaller-celled perithallium, and the 

 conceptacles with the coarse intersporangial tissue characteristic of the genus 

 Lithothamnium. 



Plate 10. 



Lithothamnium isthmi M. A. Howe. 



A specimen from about one-third mile north of New Frijoles (MacDonald 

 and Yaughan, station 6024-&, Cat. No. 35305, U.S.N.M.), natural size, showing 

 fossil embedded in matrix, in both weathered and freshly broken surfaces. 



Plate 11. 



Lithothamnium isthmi M. A. Howe. 



A somewhat obliquely transverse section of a branch (specimen from about 

 4 miles north of Gamboa Bridge, MacDonald and Vaughan, station 6021. Cat. 

 No. 35302, U.S.N.M.), enlarged 106 diameters. 



