262 BULLETIN 93^ UNITED STATES NATIONAL MUSEUM. 



FeAv of these barnacles are in the National Museum, evidently be- 

 cause the corals and millepores of the collection have not been exam- 

 ined for them. No species is positively known from American seas, 

 but P. stohcsii (Gray) Darwin has been found upon Agarlcla 

 agar'idfes, believed to be West Indian, and P. cancellatuin Leach was 

 found on a Gemmni'pord, probably West Indian, but perhaps Pacific. 



PYRGOMA ANGLICUM Sowerby. 



Cat. No. 12072. Exmouth, England, from the Jeffreys collection. 



PYRGOMA CRENATUM Sowerby. 



Jeffreys collection and I. Lea collection; one specimen in each; no 

 locality. 



Siabfamily CH:E;iL,0]SriBII]Sr^5S I'ilsbi'y. 



Balanidcc, in which the sheath extends to the base and forms the 

 whole inner wall of the body-chamber. The sutures uniting rostral 

 latera and rostrum into a. composite rostral compartment are usually 

 discernible. Compartments essentially porose, though often second- 

 arily filled up, always conspicuously lamellate at the basal edge. 

 Basis membranous. The opercular valves are much smaller than the 

 orifice ; the articular ridge of the scutum is chitinous. 



This seems to be a group of at least as high systematic rank as 

 the Coronulinse. It has a j^rimitive character in the incomplete con- 

 crescence of the elements of the composite rostrum, but in other re- 

 spects is decidedly specialized. The reduced opercular valves resem- 

 ble those of the Coronulinse superficially, but differ in their articula- 

 tions, so that no direct relationship is to be predicated from them. 

 It appears that this reduction is connected in some unexplained way 

 w^ith their habits, since it occurs in all genera living on vertebrate 

 animals. The specialization of the wall is also adaptive, but the 

 resemblance to the whale barnacles is merely superficial, as Darwin 

 has shown. 



The retention of a primitive character — the incomplete union of 

 the rostrum and rostral latera^ — is of much greater systematic value 

 in the highly evolved family Balanidse than the same feature is in 

 ihe more primitive Chthamalida?. 



Genus CHELONIBIA Leaeh. 



1817. Chelonihia Leach, Journal de Physique, vol. 85, p. 68. 



1818. Coronula Lamakck (part), Animaux sans Vertebres, vol. 5, p. 385. 

 1825. Astrolepas Klein, Gray, Annals of Philosophy, new ser., vol. 10, p. 



105. 

 1854, (JhclonoUa Dakwin, Monograph, p. 382. 





