﻿BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



type iu a nan-ower sense is the specimen sliowu at tlie lower right-hand corner 

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



Plate 2. 



Archacollthoilunnniuiii cpisporum M. A. Howe. 



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

 (Point Toro, Howe 6882). 



Fig. 1. Lithothamniiint lauahunii M. A. Howe. Photograph of the type- 

 portion of a sporangial sorus, enlarged 42 diameters. 

 2. Section, enlarged 200 diameters. 



Plate 3. 



ArcJiacolifJiothcnnniiiin. episporum M. A. Howe. 



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

 Howe 6832), enlarged 200 diameters. 



Fig. 1. Section showing sporangia and tetra spores. 



2. Section showing emptied sporangia, form and arrangement of i^eri- 

 thallic cells, a weakly developed hypothallium, etc. 



Plate 4. 



ArchaeoUthothaninium cpisporum 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. 

 ArchaeolithoHiariiniiim episponuii 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, Cat. 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. 



Arcliaeolithothamnium 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. 



