1911.] NATURAL SCIENCES OF PHILADELPHIA. 337 



Lupia perovata Conrad. 



Solarium alveatum Conrad. 



Natica eminula Conrad. 



To which the following were subsequently added : 



Corbula alabamiensis Lea. 



Corbula gregorioi Cossmann. 



The shell identified as Lupia perovata may turn out to be " Amaura" 

 guppyi Gabb, of the Santo Domingo Oligocene, a species which resem- 

 bles the Eocene form so closely that very well-preserved examples 

 are necessary for their discrimination. 



The genus Glyptostyla, represented by G. panamensis Dall, is known 

 elsewhere only from the Upper Tejon Eocene of California, where a 

 species very distinct from the Vamos a Yamos form occurs. 



The condition of the calcite pseudomorphs at Gatun is often not 

 favorable for exact determination, and it seems possible that some of 

 the identifications with Claibornian species might be modified by the 

 study of perfect examples. 3 The presence of a few Claibornian species 

 belonging to genera not characteristically Eocene in a fauna pre- 

 dominantly Oligocene does not, it seems to us, justify a reference of 

 the formation to the Eocene. Until a longer list of Eocene species 

 including some characteristic forms is made known, we are disposed 

 to regard all of the known tertiary beds of the Canal Zone carrying 

 molluscan fossils as Oligocene and as constituting one formation. 

 The exact position of the Gatun Formation among Antillean Oligocene 

 formations cannot be fixed without a more complete list of the contained 

 fossils than we now possess, but its approximate place is clear. As 

 Dall has shown, the Jamaican (Bowden) marl, by the absence of 

 Orthaulax and the greater proportion of modern species, is probably 

 somewhat later than the Santo Domingo beds. The Gatun formation, 

 as now imperfectly known, has decidedly more in common with the 

 older and more remote Santo Domingan than with the later and 

 geographically nearer Bowdenian. 



It contains many species common to both beds, and a few show 

 greater affinity to Bowden forms. Some of the difference between 

 the Isthmian and Santo Domingo faunas is doubtless due to local 

 specific differentiation; possibly this factor may account for all the 

 differences; yet on the whole we conclude that the Gatun fauna is 

 slightly later than the Santo Domingo and earlier than the Bowden. 



3 We express this possibility in view of the imperfection of the material and 

 with all respect for Dr. Dall's opinion, which is justly considered authoritative 

 in such matters. 



