100 



EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



utterly distinct from any other of our Eocene corals, and is very easily rec- 

 ognized, sinipl}' by its short cornute form and the lower alternating- costse. 



The calice is not well i)reserved, the margins of the septa being broken 

 away. The columella is apparently essential, although it is frequently fused 

 to the ends of the septa. Near their inner terminations, just before they 

 join the columella, the sejjta become thicker and fuse by slight lateral 

 outgrowths or by their margins. Pali are present, but their details could 

 not be made out. 



Trochocyathus clarkeanus (Vaughan). 

 PI. Vll, figs. 20 to 23. 



1895. Taracydthus (?) clarkeanus Vaughau. Jobus Hopkins Univ. Circ, Vol. XV, No. 



121, p. 0. 

 189G. Paracyathus (f) clarl-eanuH Vauglian. Bull. U. S. Geol. Survey No. Ill, p. 89. 



Corallum conical, usually slightly curved. Cross section elliptical. 

 Nearly always showing a distinct area of attachment, which is variable in 

 size. Costix? not very prominent; acute: 48 in number, corresponding to all 

 the cycles of the septa; nearly equal in size. In young specimens those 

 corresponding to the last cycle of septa are smaller than those earlier devel- 

 oped. No epitheca was observed and is most probably absent. 8epta thin, 

 not exsert, sides gfanulated; 48 in number, arranged in six systems of four 

 cycles each; those of the first three cycles reach the columella; the fourth 

 cycle fuse by their inner margins to the sides of the third cycle. Calicular 

 fossa shallow. Pali appai-eutly before all of the cycles of the septa except 

 the last, small and thin, and appear to lie arranged in two crowns. Rudi- 

 mentary dissepiments apparentl}- present. Columella fascicular; upper 

 surface papillate. 



The measurements of the two specimens are: 



Greater diameter of calice 

 Lesser diameter of calice . 

 Height of corallum 



7 



6 



12.5 



Mm. 

 7.75 

 5.5 

 9.75 



Localities. — Potouiac Crcck and Aquia Cret'k, Virginia. 

 Geologic occurrence. — Pamuukcy formation, Aquia Creek beds. 



