THE SESSILE BARNACLES. 101 



1906. 'Balanus concavus Bronn, DE ALESSANDRI, Palseontographia Italica, vol. 

 12, p. 295, pi. 16, figs. 21-25; pi. 17, figs. 1-4. 



Type-locality. Andona Valley, near Asti, Piedmont. Pliocene. 



Distribution. Oligocene to Pleistocene of Italy. Pliocene of Eng- 

 land and Portugal. Various races or subspecies in the Miocene and 

 Pliocene of the United States. Other races recent from California to 

 Peru and in the Philippines. 



Balanus concavus, in the broad sense, was an abundant barnacle 

 throughout the Neocene in both hemispheres. In the Miocene, 

 when our definite information begins, there were several strongly 

 individualized races, possibly species, but here ranked as subspecies. 

 These continued, in their several areas, into the Pliocene with more 

 or less change; in the Mediterranean basin they endured into the 

 Pleistocene. The total disappearance of the group from Recent 

 Atlantic faunas does not seem explicable at present. 



The typical form of B. concavus, as figured by Bronn and recently 

 treated in detail by De Alessandri, is conic or convexly conic, with 

 the orifice more or less contracted, or often cylindric with large orifice. 

 The summits of the radii are very oblique, and the parietes are usually 

 ribbed, not very strongly, or variously roughened. Sometimes it is 

 smooth. The Pliocene examples often show color-stripes. De 

 Alessandri, who studied Italian specimens from Oligocene (Tongrian 

 of Sardinia) to Pleistocene, does not record any change throughout 

 the duration of the species in that area a remarkable constancy if 

 really the fact. I believe, however, that he had not seen the opercu- 

 lar valves of the Oligocene form. 



The British Red Crag examples (pi. 21, figs. 1, Ic, from the Jeffreys 

 collection, Cat. No. 12058, U.S.N.M.) are practically typical, but they 

 perhaps vary somewhat from the Italian by having the tergum 

 sometimes narrower, with a longer spur. My plate 21, figure 1&, is 

 very similar to one of De Alessandri's figures (pi. 4 , fig. 21) of a 

 topotype. 



The scutum has rather coarsely latticed sculpture, the longitudinal 

 strise often divided, and obsolete on the roundly inflected tergal 

 margin. The basitergal angle is cut off. The adductor ridge is 

 quite short and not very prominent. The inner border of the rather 

 deeply sunken depressor muscle pit is slightly prominent, but not 

 raised into a ridge. 



This European form was an abundant Pliocene barnacle of that 

 area, where it seems to have existed almost to the present time. It 

 has not been found in America, where various other races of the 

 species existed, and is noticed here merely for comparison with the 

 latter. 



Our definite knowledge of East American barnacles of the concavus 

 type begins with the Miocene, continuing to the Pliocene, when the 

 4729 Bull. 9316 8 



