430 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



The three species, naming them in geologically ascending series, A. 

 anguillensis, A. dominicensis, and A. nobilis, seem to form an evolu- 

 tionary series, the lower side of the calices becoming progressively 

 more produced and more prominent, while the alternation in the size 

 of the septa and the septo-costae increases. 



Genus PAVONA Lamarck. 



1801. Pavona Lamarck, Syst. Anim. sans. Vert., p. 372. 



1917. Pavona Vaughan, Carnegie Inst. Washington Pub. 213, p. 132. 



Type-species. — Pavona cristata Lamarck— Madvcpora cristata Ellis 

 and Solander = Madrepora cactus Forskal. 



PAVONA PANAMENSIS, new species. 



Plate 110, figs. 1, la, 16, 2, 2a, 3, 3a, 



This species is so variable that formal descriptions of the two 

 extremes will be presented. 



The first specimen to be described (pi. 110, figs. 1, la, lb) is from 

 station 6016, Empire, Canal Zone. 



Corallum massive or forming thick plates, maximum thickness of 

 type 37 mm. 



Calices in more or less definite series; diameter, about 4 mm. ; 

 distance between series as much as 3.5 mm. Intercalicular areas 

 arched or flat. 



Septa strongly alternating in size; about 10 prominent, tall septa 

 reach the columella; between each pair of these is a lower, smaller 

 septum, occasionally three small between two larger septa; edges of 

 the larger septa steep around the columella fossa. 



Septo-costae continuous from calice to calice, strongly alternating 

 or in places subequal in size; synapticulae visible between them. 



Columella formed by the fusion of the inner ends of the large septa ; 

 in some calices it appears to be a central tubercle. 



Dissepiments well developed ; 7 within 4 mm. 



The next specimen (pi. 110, figs. 2, 2a) is from station 6015, also in 

 Empire, Canal Zone. 1 



Corallum forming nodular masses or encrusting dead coral or other 

 such objects. The size and form are shown by plate 110, figures 2, 

 2a. Another specimen has an attached base and flat upper surface. 



Calices irregularly distributed or in short, indistinct series; diameter 

 of the apertures usually range between 2 and 3 mm., as the outline in 

 plan is subelliptical or oval the two diameters at right angles are 

 rarely equal in the same calice; depth about 1.5 mm. ; distance apart 

 ranges from a mere dividing wall up to 2.5 mm., about 1 mm. usual. 

 Intercalicular areas flat between fully developed calices. 



Septa, number in fully grown calices 24 to 26; of these about half 

 or more than half extend to the columella; around the calicular edge, 



i Compare the illustrations of this specimen with the figures of D'Achiardi's Reussastraea granulosa, 

 Corall. eocen. Fruli, p. 67, pi. 13, figs. 2a, 2b, 2c, 1875. Reussastraea is a synonym of Pavona. 



