6 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



The height of the cavities ranges from about 8m to 1 5/x ; the length 

 from about 25fj. to 65^. The roofs are finely perforate and are from 

 about 8m to 25/x thick. The appearance is that the roofs exceed the 

 cavities in thickness, but some of this appearance is probably due to 

 secondary thickening. The pillars show as thickenings of the roofs 

 one above another. 



Locality and geologic horizon. — Plaza, San Antonio, State of San 

 Luis Potosf, Mexico, Basal part of the Chicontepec formation. 

 The specimens were received from Paul Weaver, formerly chief 

 geologist of the Aguila Company, for whom it is a pleasure to name 

 the species. 



Cotypes.— Two entire specimens (Cat. No. 371006, U.S.N.M.) and 

 two thin sections, one horizontal and one vertical, deposited in the 

 United States National Museum. Other specimens in the Scripps 

 Institution. 



There are in the collection numerous specimens that represent 

 variants of this species. One specimen, 2.75 mm. in diameter and 

 1.5 mm. thick, with a strongly papillate surface, is an inflated variant. 

 In a second variant the top of the central dome is narrower than in 

 the typical form and there is a slight thin edge. A third variant is 

 not so thick as the tj^pical form and the papillae are smaller. Three 

 specimens have the following measurements: Diameter (a) 2.5, (b) 

 2.5, (c) 3.5 mm.; thickness, (a) 0.75, (6) 0.75, (c) 1 mm. The papil- 

 lae are from 80/x to lOO/i thick. The differences from typical speci- 

 mens are of degree rather than of kind. 



The best horizontal section of this species is of the last-mentioned 

 variant — that is, the slightly thinner variant with smaller papillae — • 

 and it will be described in detail. For illustration see Plate 1 , figure 1 . 



The embryonic apparatus consists of an initial chamber entirely 

 enveloped by a second chamber, except on one side, where the initial 

 chamber is attached to the inside of the wall of the second chamber. 

 The longer diameter of the initial chamber is perpendicular to the 

 line of its attachment and measures 127^. The diameter at right 

 angles to the preceding is 105^- The length of the line of attach- 

 ment is about 53/x. The wall is about 7/i thick, and it is finely 

 perforate. The diameter of the two chambers along the longer axis 

 of the initial chamber is about 200/x; at right angles to that line it 

 is about 220m. The wall is about 15m thick, except near the 

 attachment of the interior chamber, where it is thinner. It is per- 

 forated by rather large passages, which measure as much as 5/i 

 across. These passages precisely simulate the interannular connec- 

 tions, which may be seen in many places at the sides of the radial 

 chamber walls. 



The embryonic apparatus is entirely surrounded by a first annulus 

 of the kind, not quite complete, described for a cotype of the species 



