BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



type in a narrower sense is the specimen shown at the lower right-hand corner 

 of the plate — the specimen from which figure 1 of plate 5 was obtained. 



Plate 2. 



ArchaeolithotJioninium episporum M. A. Howe. 



Photographs of radio-vertical ground (calciferous) sections of type material 

 (Point Toro, Howe 6882). 



Fig. 1. Lithothammtim vauyhanii M. A. Howe. Photograph of the type- 

 portion of a sporangial sorus, enlarged 42 diameters. 

 2. Section, enlarged 200 diameters. 



Plate 3. 



ArcluieoUtlwtliamnium episporum M. A. Howe. 



Photographs of radio-vertical sections of decalcified material (Point Toro, 

 Howe 6832), enlarged 200 diameters. 



Fig. 1. Section showing sporangia and tetraspores. 



2. Section showing emptied sporangia, form and arrangement of peri- 

 thallic cells, a weakly developed hypothallium, etc. 



Plate 4. 



Arcliaeolithotliamnium, episporum M. A. Howe. 



A Pleistocene fossil, " from flats near Mount Hope, five feet above tide level," 

 D. F. MacDonald 6039, 1911, natural size. 



Plate 5. 

 ArchaeoKtliotliamnvum episporum M. A. Howe. 



Figs. 1 and 2. Photographs of the type material (Point Toro, Howe 6832). 



Fig. 1. Portion of the surface, showing the more or less confluent sporangial 

 sori, enlarged 4 diameters. 

 2. A smaller part of the same surface, showing the sporangial ostioles, 

 etc., enlarged 25 diameters. 

 Figs. 3 and 4. Photographs' of Pleistocene specimen from Mount Hope (Mac- 

 Donald, Oat. No. 35298, U.S.N.M.) 

 Fig. 3. Radiovertical section showing several superposed crusts and three well- 

 developed hypothallia, enlarged 42 diameters. 

 4. A part of a cross section of one of the excrescences or branches, showing 

 a single weakly developed hypothallium, enlarged 42 diameters. Com- 

 pare structure of living specimen as shown in fig. 1, plate 2. 



Plate 6. 



Archaeolithothamnium episporum M. A. Howe. 



Photograph of section of the Pleistocene fossil from near Mount Hope 

 (Cat. No. 35298, U.S.N.M.). A section magnified 73 diameters. 



