THE SESSILE BAKNACLES. 267 



CHELONIBIA CARETTA (Spengler). 

 Plate 63, figs. 5, Or/, 



1790. Lcpas carclta SPENGLER, Skrifter af Naturhist, Selskabet, vol. 1, 



p. 185, pi. G, fig. 4. 



1825. Astrolepas tcfttudinaria GRAY, Annals of Philosophy, vol. 10, p. 105. 

 1840. Balanus chclytrypetes HINKS, Annals of Natural History, vol. 5, pp. 



333-4. 



. Coroniila sulcata CHENU, Illustrations Conchyliologiques, pi. 1, fig. 1. 



1854. Chelonobia carctta DARWIN, Monograph, p. 394, pi. 14, fig. 2. 



According to Darwin 



The descending sheath and radiating septa are of very variable thickness and 

 have their basal edges finely dentated. The septa are not continuous from the 

 circumference to the sheath in unbroken plates, but are irregularly divided into 

 separate, often short, portions and even occasionally into mere points. The 

 sheath differs from that of the other two specimens in having loopholes for the 

 entrance of ribbons of corium only on the eight lines of suture, and not, with 

 rare exceptions, in the middle of each compartment. This is evidently due to 

 fewer filaments of corium being here sufficient to supply the less deep inter- 

 spaces between the radiating septa, for in this species there are no flattened 

 cavities or tubes running far up the shell. The inner lamina of the walls can 

 not be here distinguished, for a solid, flat calcareous surface extends from the 

 circumference between the radiating septa to the sheath. The sheath, had it 

 not been from the light thrown on this part by the other species, would have cer- 

 tainly been mistaken for the inner lamina of the walls. Tlie absence of tlie 

 flattened cavities or tubes extending up tlie parietes seems to be the least vary- 

 ing character and serves to distinguish this species from those worn and massive 

 specimens of C. testiiiUnaria, which have narrow and not-notched radii. 



The opercular valves hardly present any essential difference, compared with 

 those of the other species, but the occludent margin of the scutum is apt to be 

 more sinuous and its rostral end blunter and squarer. The carinal end of the 

 tergum is also squarer than in any common variety of C. tcstudinaria, the 

 external furrow or spur near the carinal margin is very indistinct, and even 

 sometimes is quite absent. 



Distribution. Darwin had this species from the west coast of 

 Africa and northern Australia. Doctor Weltner reports it from Vene- 

 zuela, Massaua, and Torres Strait. The Paris Museum has speci- 

 mens from Cape of Good Hope and Saigon. Specimens are in the 

 collection of the Academy of Natural Sciences, Philadelphia, from 

 St. Thomas, West Indies, taken by Robert Swift, and from a logger- 

 head turtle from Delaware Bay, New Jersey, taken by myself. These 

 examples are very small and flat, 13 mm. long, and nearly covered by 

 the shell of the turtle. Equally small examples of C. testudinaria on 

 the same turtle were not at all embedded. Those in the United States 

 National Museum are from " East Indies," I. Lea collection, and 

 Cape Frio, Brazil, collector not recorded. It appears to be chiefly 

 tropical. Records from the central and eastern Pacific are lacking. 



