igog.] N. AnnandaIvE : The Indian Cirripedia Pedunculata. 125 



be detected with the aid of a high power of the microscope, others in which this body 

 can just be seen with a hand lens, others in which it is larger and definitely though 

 narrowly triangular, and others again in which the base is broadened out so as to form 

 a second triangle; in a few the lateral angles of this triangle are lengthened into short 

 branches. So far as the carina is concerned, the only point at which a break occurs 

 in the series is the one at which it is possible to distinguish the base as a triangle ; 

 but this break is a very small one. 



In some specimens it is possible to distinguish near the apex of the capitulum a 

 chitinous structure of a yellowish colour which obviously represents the tergum. It 

 never has a definite outline but fades imperceptibly into the surrounding membrane. 

 In many individuals it is quite absent and in others it is only faintly indicated. 



The scutum in its simplest form is a narrowly linear, sinuous structure at the 

 side of the aperture. Often the two scuta of an individual difïer in length. In a large 

 proportion of the individuals I have examined a short piece of the lower end of the 

 valve forms an angle with the slanting or tranverse portion at the side of the aperture. 

 In a few specimens this lower branch of the scutum has a more considerable length, 

 and in one specimen it is completely separated from the upper branch. In several the 

 upper branch is noticeably broader than the lower one, but this is a rare occurrence. 

 The angle at which the two branches meet is generally greater than a right angle, 

 but in several of my specimens it is less. 



The next question to be answered is, how far are the differences in one valve 

 correlated with those in the others ? Speaking generally, I may say that the develop- 

 ment of the lower branch of the scutum corresponds, as a rule, with that of the basal 

 branches of the carina. But this rule is not without exceptions, for the specimen 

 in the Museum in which the basal branch of the scutum is best developed possesses a 

 carina that is small and narrowly triangular as a whole. I have not seen an indivi- 

 dual without a carina, however, in which the basal branches of the carina were 

 apparent. The absence or presence of a chitinous tergum is not a character that 

 can be correlated with any other. 



External characters are not the only ones on which D. angulata, D. aperta, 

 D. cnneata, D. hullata and D. transversa were originally separated from one another. 

 Aurivillius lays considerable stress on the length of the anal appendages relative to the 

 joints of the protopodite of the sixth cirrus, and also on the number of teeth on the 

 mandible . He shows himself , however , that the former is a variable character in another 

 species of the genus, namely, D. warwickn {op. cit., pi. 8, figs. 20, 21), and I do not 

 find it constant in any species of Dichelaspis or Pœcilasma of which I have been able to 

 examine more than one or two examples. In these genera, moreover, the number 

 of teeth on the mandible is frequently variable, sometimes being different on the two 

 mandibles of one individual. This fact has been recognized in the published descrip- 

 tions of some species and ignored in those of others, probably because the description 

 is often based on the examination (or at any rate the dissection) of a single specimen. 

 C. W. Aurivillius' s descriptions of the cirri, etc., are very short, so that it is difficult 

 to regard them as a basis for comparison ; while he rarely mentions the penis. The 



