THE SESSILE BAKNACLES. 2G3 



Compartments generally extremely thick, six, but the rostrum is 

 composed of three very intimately united compartments, the sutures 

 visible internally and in Avorn specimens also on the outside. 

 Parietes porous (septate), but sometimes filled up solidly nearly to 

 the bases of the septa. Basis flat, membranous; opercular valves 

 narrow, not nearly closing the orifice, the scuta and terga united by 

 a chitinous articular ligament (pi. 62, fig. 6). Labrum having a long 

 row of teeth and a median notch in the margin. Third pair of cirri 

 long, but structurally like the second; later cirri long, having seg- 

 ments with two pairs of spines, with little tufts of fine spines between. 



Type. C. testudinaria (Linnaeus). 



Distribution. Tropical and temperate seas, on turtles, crabs, and 

 manatees. Pliocene of Grand Canary and Italy. 



This group retains a primitive character in the incompletely con- 

 crescent rostrum and rostro-lateral compartments. The sutures may 

 be traced on the inside and in worn individuals externally. It is 

 a transition from the octomerous stage to the hexamerous. In other 

 respects it is rather highly specialized. In the least modified species, 

 C. patula, the structure of the Avail reminds one of Balanus, but I 

 venture the opinion that the resemblance is probably due to con- 

 vergence, the structures being homoplastic. The more specialized 

 species are admirably adapted to the rough conditions of existence 

 on the backs of sea turtles, the Avails being enormously thickened and 

 the stature low. They have a superficial resemblance to the whale 

 barnacles, Coronula. 



C. testudinaria is attached superficially, and when removed the 

 turtle shell is found quite smooth and uninjured. It is the same 

 with C. patula on crabs. In C. caretta the groAving peripheral edge 

 cuts into the turtle shell, Avhich commonly covers or curves up over 

 the edges of the barnacle. DarAvin quite appropriately compares 

 this penetrating POAVCT of the barnacle to that of growing roots. 



Clielonobla patella (Ranzani) 1 is evidently a pen error for C. 

 patula. 



The f olloAving fossil species have been described : G. hemisp/iccrica 

 Rothpletz and Simonelli, 2 Pliocene of Grand Canary; C. emixpha- 

 rica De Alessandri, 1906. C '. dcpressa Seguenza, 1875, Pliocene of 

 Sicily. C. capellinii De Alessandri, 3 Miocene and Pliocene, Italy. 



All of them are of the testudinaria type, and therefore afford no 

 information on the phylogeny of the genus. The recent C. patula 

 is the most primitive of the known species in structure. 



1 Zoologischer Anzeiger, vol. 38, p. 461, November, 1011. 



- Zeitschrift deutsch. Gool. Ges., vol. 42, 1891, p. 724, pi. 36, fig. 2. 



3 Palaeontographica Italica, vol. 12, 1906, p. 313. 



