THE SESSILE BARNACLES. 287 



Darwin seems to have included barnacles varying a good deal in 

 shape in this species, though the existing descriptions and illustra- 

 tions give only an inadequate idea of the forms seen by him. There 

 is a small individual in the Isaac Lea collection, United States 

 National Museum, from Sicily, which probably represents a sub- 

 species (pi. CT, fig. 4). It has steep, convex sides, deep median 

 clefts in the compartments, but the internal midribs are slender 

 and project but little. The septa are very numerous, sharp, and 

 close; greatest diameter, 8.5 mm.; height, 4.8 mm. From the ap- 

 pearance of this barnacle I suspect that it did not live on the shell 

 of a turtle. There is some orange-colored skin adhering in the 

 furrows of the lower part of the parietes. 



/'. h. irfifJi'/oj'hila, new variety, plate 67, figure 2. Specimens taken 

 by Mr. Joseph Willcox from a Lepisosteus caught in brackish water 

 in Hernando County, Florida, are small, very thin, and delicate, oval 

 or rounded, 7 to 8 mm. in diameter. The rugae of growth are re- 

 duced, and on some compartments absent. Median sulci of the com- 

 partments shallow, probably on account of immaturity. The inter- 

 nal midribs or props are more slender than in P. hexastylos, scarcely 

 sculptured. Internal septa of the edge much less numerous than in 

 hcxa-stylos, and projecting toothlike at the edge. There are four 

 or five principal septa on each side of the midrib in the rostrum 

 (pi. 67, fig. 2). 



So far as I know this is the only record of a barnacle attached 

 to a fish.' It was identified as Platylepas decorata Darwin by Dr. 

 John A. Ryder. 1 



CYLINDROLEPAS, new genus. 



Form cylindric, the orifice and base of equal size; bases of the 

 compartments obtusely dentate, the median tooth of each compart- 

 ment larger, slightly inflected; sheath very long, not quite reaching 

 to the base. Basis and opercular valves as in Platylepas. Living 

 embedded up to the orifice in the skin of turtles. 



By its deep embedment and small size this barnacle resembles 

 StepTumolepaS) but it differs by the strictly cylindric shape and the 

 denticulation of the bases of the compartments; StepJianolepas being 

 cup-shaped, the base much smaller than the orifice, and the basal 

 edge not dentate. The prominent midribs of the compartments of 

 Platylepas are represented in Cylindrolepas by slight prominences 

 of the basal borders vestigeal structures, now useless in consequence 

 of the altered shape of the barnacle. Unlike Platylepas, the sheath 

 is nearly as long as the compartments. 



Type. G ylindrolepas darwiniana, new species. 



1 American Naturalist, vol. 1.,, July, 1879, p. 453 



