^00 PROCEEDINGS OF THE ACADEMY OF [NoV., 



finding of the same species in both the tuffs and the white limestone 

 would point to their forming really but one geological unit, "although 

 characterized by great changes in the physical conditions during the 

 accumulation of the system." What has been said of the gradual 

 passage of the upper shales and tuffs into the marls and their apparent 

 ■conformability point to these formations forming one geological 

 unit. As to the age of the corals examined by Dr. Vaughan, he 

 notes that the coral fauna of the Antigua formation "is identical 

 with that of the lower beds of the upper Oligocene formation of 

 southwestern Georgia." 



The mollusks collected by Spencer were referred to Dr. Dall, who 

 afterwards determined one of the forms as Peden (Chlamys) anguil- 

 lensis Guppy, and described one as Peden (Plagiodenium) gahhi 

 Dall, referred to below in the list of species in the collection made by 

 me in Antigua. 



Professor Gregory,^- lists two species of echinoids sent to him by 

 Mr. Forrest, and these are also among the species collected by me in 

 Antigua. They are, as given by Gregory, Echinanthus concavus 

 (Cott.) and Echinanthus antillarum (Cott.). With the exceptions of 

 the two Pectens noted above, as determined by Dr. Dall, no mollusks 

 appear to have been recorded from this Antigua white limestone, 

 so that the few which I was able to secure will help to fix the age of 

 the formation. The limestones in some places carry many species 

 of Pectens, and as these are frequently determinable even in frag- 

 ments, more attention was given to collecting them than to corals, 

 foramenifera, etc. Although difficult to extract from the rock, I 

 was fortunate enough to obtain five known species or varieties of 

 Oligocene Pectens as well as two new species of this genus, and a new 

 species of oyster, a Turritella, and six or seven species of echinoids. 

 These, with the corals that have been determined as Oligocene, will 

 serve to confirm the age of the formation. The list of species col- 

 lected from* this Antigua formation is given below. 



Species collected from the Antigua Formation. 

 Diplothecanthus concavus (Cott.). 



Clypeasier concavus Cott., 1875.— Cotteau, Kongl. Sv. Vet. Akad. Hand- 



lingar, B. 13, No. 6, p. 16, pi. II, figs. 4-8. ^ , c, t , 



Echinanthus concavus (Cott.).— Gregory, Quart. Jour. Geol. boc. London, 

 Vol. LI (1895), p. 295. 



This is the commonest echinoid in the Antigua white limestone, 

 " Gregory, Quart. Jour. Geol. Soc. London, Vol. LI, 1895, p. 295. 



