252 DISCOVERY REPORTS 



parasitic copepod Pennella from a Blue whale. Hoek (1909) notes a similar occurrence 

 of the species. It is certainly to be found on many other animals. 



The individuals from the ship's sides, 8. xi. 25, 2° 02' 09" N, 12° 33' 00" W, were 

 collected thirty-four days after the ship left England. Their measurements were: length 

 of capitulum 19 mm., breadth 12-5 mm.; length of peduncle 22 mm., breadth 9 mm. 



Genus Hexelasma, Hoek, 1913 



Hexelasma corolliforme (Hoek, 1883). 



Balanus corolliformis , Hoek, 1883, Challeng. Rep. vin, p. 155; Gruvel, 1905, Monogr. Cinhip. 

 P- 255- 

 St. 175. 2. iii. 27. Bransfield Straits, South Shetlands. 63° 17' 20" S, 59° 48' 15" W. 200 m., 

 m. St. g. Gear DLH. One specimen. 



Distribution. Kerguelen and South Shetland Islands. 200-280 m. 



Supplementary Description. Of this genus Hexelasma, created by Hoek in 1913, 

 eight species are known. The species here dealt with was first regarded by Hoek as a 

 Balanus. The Discovery specimen is a little smaller than that figured by Hoek. The 

 external shape of the type differs in the more developed plates in the wall, and in the 

 consequent wider orifice. This is due only to a difference in age.^ 



The shell in this specimen is covered by a brown membrane with chitinous spines 

 situated on the growth ridges, and this is in agreement with the description of Hoek. 

 After removal of this membrane the compartments are seen to be white. 



The parietes are here fully figured and described. 



Carina little more than half the breadth of the scutum, with distinctly indicated alae. 



Carino-lateral compartments rather narrow, with a distinct ala on the lateral side. 

 No radius visible externally. On the inside of this part a longitudinal depression is 

 formed where the plate overlaps the carina. 



Lateral compartment about twice as wide as the carino-lateral, and with a distinct ala 

 on the rostral side. No external radius is here differentiated, but the plate covers the ala 

 of the carino-lateral plate. 



"Rostrum" constituting the broadest plate in the wall, with internally marked 

 longitudinal furrows, against which the alae of the lateralia abut. This plate is held by 

 Pilsbry (1916) and Withers (1928) to be composed of a real rostrum and two rostro- 

 laterals. As the genus in all respects is a typical Chthamalid, the real rostrum ought to 

 have alae. 



The compartments of the wall in these specimens seem to be nearly of the same length. 

 The "rostrum" is here somewhat longer than the carina. In some other species of 

 Hexelasma the carina is longer than the rostrum {H. antarctictim, Borradaile, 1916, and 

 H. americanum, Pilsbry, 1916). In this species I am unable to find any traces of a sheath 

 which, in other Hexelasma species that have been described, is distinctly indicated. 

 Hoek's specimens, to judge by his figure, seem not to have such parts. 



1 Since writing the above I find that H. hirsiituin (Hoek, 1883) must be regarded as a synonym of 

 this species, of which it is a younger stage. 



