GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 9 



perithallium abrupt; medullary hypothallium of the branches mostly 

 0.6-2.0 mm. in diameter, often turning yellow and more or less disin- 

 tegrated, its cells 17-44 \>. by 8-13 |x, transition to the perithallium 

 abrupt or gradual: cells of the perithallium in distinct layers, the 

 layers in rather indistinct zones; perithallic cells of the crustaceous 

 parts subquadrate, 8-11 \k in diameter, sometimes only 6 \l broad; 

 perithallic cells of the branches usually a little higher than broad, 

 8-19 p. by 8-12 ^ ; conceptacles becoming embedded ; tetrasporic con- 

 ceptacles appearing much flattened in a vertical section, the cavity 

 240-550 \l in maximum width, 130-165 [>. in height. 



Localities and geologic occurrence. — In Emperador limestone of 

 Oligocene age (and often constituting the dominant element in its 

 composition) on relocated line of the Panama Kailroad, opposite San 

 Pablo, Panama Canal Zone (" first limestone outcrop just north of 

 Caimito Station, about four miles north of Gamboa Bridge"), col- 

 lected by D. F. MacDonald and T. W. Vaughan, 1911, Station No. 

 6021 (No. 35301, type); and "above foraminiferous marl at Agua 

 Salud Bridge about | mile north of New Frijoles on relocated line, 

 Panama Railroad," by the same collectors, Station No. 6024?>. 



Holotype and paratypes. — Cat. Nos. 35301 to 35303, U.S.N.M. 



The material upon which the above description is based shows 

 much variation in form and structure and it was our first impression 

 that two or more species were represented in it. However, if this is 

 true, the two or more species are so intergrown and entangled and 

 are so similar in structure that it is difficult to determine where one 

 begins and the other ends. As regards the vegetative structure, we 

 believe that we have been able to trace the continuous organic con- 

 nection of the two types shown in our photomicrographs (pi. 9 and 

 fig. 2, pi. 11), yet it is notoriously easy in the case of overgrowing 

 and overgrown fossil Lithothamnieae to mistake the close contact of 

 independent plants for structural continuity. 



In the tetrasporangial specimen (No. 35301 — fig. 3, pi. 7 and pi. 9) 

 that we have named as the type, the thallus presents itself in the 

 form of irregularly superposed crusts, more or less overlaid by 

 crusts showing a somewhat different structure and conceptacles of 

 a different sort, these outer layers probably representing a crustace- 

 ous species of LithophyUum. The hypothallium of this No. 35301 is 

 suggestive of that figured by Foslie 1 for his living Lithothamnium 

 fragilissimum from Borneo (which, however, has a much thinner 

 thallus). It suggests also the hypothallium of Lithothamnium lich- 



1 Foslie, M. Lithothamnioneae, Melobesieae, Mastophoreae. In Weber-van Bosse, A., 

 and Foslie, M. The Corallinaceae of the Siboga Expedition, Siboga Exped. Monog. No. 61, 

 fig. 5, 1904. 



