216 PROCEEDINGS OF THE ACADEMY OF [May, 



are living to-day in the Indo-Pacific region. In its apical features, 

 then, P. pilshryi has attained about the same evolutional grade as 

 several of the recent forms. 



Nevertheless there is in the Oligocene or Miocene at least one excep- 

 tion to the general prevalence of the primitive apex. This is furnished 

 by the Pyrida far6asm(?), which in addition to the feature already 

 mentioned has a specialized adult sculpture that marks it as an early 

 offshoot from the main stock, and it is probably also a terminal member 

 of such an offshoot. 



Passing over this aberrant form, we find that in the Pliocene rocks of 

 North America the smooth stage is still further restricted and the apex 

 3'et larger, for there is at least one subspecies of Pyrula jxipyratia. 

 It is more primitive than the recent P. papyratia, for the first whorl is 

 hardly as large and the cancellated stage is not quite so accelerated as 

 in the recent form. It is very close and must be regarded as ancestral 

 to P. papyratia of the modern Florida seas. 



In American rocks, then, we have an excellent series showing the 

 gradual acceleration of the sculpture and the increase in size of the 

 early whorls. With the exception of P. mississippiensis and P. 

 carbasea this American series represents a good morphological succes- 

 sion, and from P. pilshryi to the living P. papyratia we can reasonably 

 assume a phylogenetic succession as well. 



The solution of the ancestry for the present day species of the Indian 

 and Pacific Oceans can hardly be attempted with the meager data at 

 our command. Pyrula decussata, P. dussumieri, and P. ficus probably 

 owe their origin to some such generalized types as we have seen in the 

 American Eocene and the European jMiocene. Just how long their 

 separate specific stocks have been distinct it is impossible to say. The 

 forms described as P. reticulata probably represent a group of geo- 

 graphical races which have arrived at different stages of evolution. 

 Some of them are very like Pyrula condita of the Miocene, for the 

 ribs are strong and, equalling the primary spirals, impart a markedly 

 cancellated appearance to the shell. Pyrida tesscllata of Australian 

 seas represents an offshoot from the primitive stock. It has become 

 distinctive by its large swollen apex and the encroachment upward of 

 each whorl high on its predecessor; but its ribbing is relatively strong, 

 the sculpture of its cancellated stage being primitive. 



A point of great interest is the succession of morphological features 

 which has taken place in the Gulf and Caribbean region with the 

 progress of the Tertiary. Pyrula pilshryi is more specialized than the 

 Eocene forms, but less specialized than the later races which are 



