578 NEW YORK STATE MUSEUM 



fers only by the stronger elevation of the concentric lines, is re- 

 stricted to the upper Devonic (Cleveland shales), while T u r - 

 rilepas (?) filosus occurs in the middle Lower Silurio. 

 The occurrence of these valves of equal structure at such widely 

 separate epochs can serve only to strengthen the belief in their 

 representing a different and persistent type of crustacean struc- 

 ture. 



Pollicipes siluricus sp. n. (pi. 2, fig. 16-24). 



In the Utica shales of Green Mand and Mechanicsville occur 

 variously shaped valves in considerable number, which by their 

 peculiar shapes, the arrangement of their growth lines and their 

 shell structure, differ from the valves of all mollusks associated 

 with them in the same rock. A suggestion of Dr Clarke as to 

 their possible crustacean nature led to the astonishing discovery 

 that they all find their homok)gues in parts of the capitula of 

 the pedunculate cirriped genera S c a 1 p e 1 1 u m and Pol 1 i - 

 c i p e s, notably of the latter. On this account the various 

 valves have been united under the caption, Pollicipies 

 siluricus, in full consciousness of the enormous gap exist- 

 ing between the appearance of this Lower Siluric type and the 

 next Upper Triassic (Rhaetic) representatives of these genera. 

 But the analogous case of the related Balanidae might be cited 

 in support. Charles Darwin, in his classic memoir on the fossil 

 Cirripedia,! stated that in the sessile Cirripedia, or Balanidae, 

 the negative evidence of their not being found in primary or 

 secondary formations is of considerable value, considering their 

 great number where they appear, their strong shells, etc.; and 

 yet, meanwhile, undoubted Paleozoic genera of Balanidae (P r o - 

 tobalanus, Palaeocreusia) have been found, leaving 

 the long interval from the Devonic to the Cretaceous without 

 any representatives of this family. It is an interesting query, 

 what were the conditions of marine life that suppressed the Lepa- 

 didae and Balanidae, which today fill the oceans with such vast 



*A monograph of the fossil Lepadidae, or pedunculated cirripedes of 

 Great Britain, Palaeont soe. 1851. 



