E. W. MAcBRIDB AND J. C. SIMPSON. 

 3. ECHINOPLUTEDS ANTARCTICUS. 



(Fig. 3.) 



The material contained only two specimens of this larva : one taken in 

 lat. 78 29' 10" S., long. 103 38' 18" W., on January 25th, 1902, and labelled "30," 

 the other marked " 42," taken in the D-net at Hut Point, near the Winter Quarters 

 of the Expedition, on February 19th of the same year. Both specimens are of 

 approximately the same age. 



In the stained, and mounted condition the specimens measure 072 and 0'84 mm. 

 in length, including the arms ; but in each case the body, which is sub-spherical in 

 form, is 0'43 mm. in diameter. 



Four pairs of arms can be made out ; of these, the post-oral pair are the longest, 

 being a little more than two-thirds as long as the body. Of the others, the antero- 

 laterals are about half and the postero-dorsals about one-quarter the body-length. 

 The pre-oral arms are very rudimentary, appearing only as small outgrowths at the 

 bases of the antero-laterals. All the arms are close together and are approximately 

 parallel. 



The ciliated band, which borders all the arms, extends back between the post-oral 

 and postero-dorsal arms of either side, so as to form lateral bays running about half 

 way along the body. 



Three pairs of epaulettes are present, and are arranged so as to form two 

 incomplete ciliated bands encircling the body. The anterior circle consists of a 

 ventral pair situated at the bases of the post-oral arms, and a dorsal pair in a 

 somewhat corresponding position on the dorsal surface of the body at the bases of the 

 postero-dorsal arms. The posterior circle is made up of a single pair only, and these 

 are smaller and much narrower than either of the other pairs, and are laterally placed 

 near the posterior end of the body. 



We find that three Echinoplutei have been described in which the presence of 

 six ciliated epaulettes is noted. These are : E. coronatus, E. theeli, and the pluteus 

 of Echinus esculentus. From each of these, however, the present larva differs 

 considerably. In Echinus esculentus the presence of the posterior pair of epaulettes 

 was first pointed out by MacBride (8), and a great deal of material of the larvae of this 

 species has been at our disposal for comparison with our new type. Selecting an 

 individual which, judging by the development of the so-called " Echinus-rudiment," 

 is of the same age as our specimens of E. antarcticus, we find that the size of the 

 characteristic larval arms is quite different. The post-oral and postero-dorsal pairs 

 are of about the same length, and are already about twice as long as the body, instead 

 of two-thirds and one-quarter the body-length, as they are in E. antarcticus. The 

 antero-laterals are also of great length, being more than twice as long in comparison as 

 are the corresponding arms in our new species. The most marked difference, however, is 



