HALATRACTUS NANUS AT PLYMOUTH. 



405 



The specimen agrees fairly well with the descriptions of Alder, 

 Hincks, and Allman as completed by Bonnevie (1899). Nevertheless, 

 I give here an accurate drawing (Plate YII), since it differs from the figure 

 given by Hincks in many details, and the species has, indeed, never been 

 adequately figured. The base is unfortunately broken off. The whole 

 individual has a length of 3"5 mm. ; the lower diameter of the hydranth, 

 measured between the bases of the tentacles, is 0'8 mm. ; the aboral 

 tentacles are about I'b mm. long. The specimen is a young one, as can 

 be seen by the immature condition of the gonophores. These show 

 the beginning of the invagination of the Entocodon (" Glocken- 

 kern "), with as yet no trace of a differentiation into the characteristic 

 medusoid organs (Fig. 1). The gonophores are simple and v.nhranched ; 



Fig. 1. — Halatractus nanus (Alder). Blastostyle (Diagrammatic, with outline drawn 

 from actual preparation. The " Glockenkern" is dotted). 



they do not hang in bunches, as is characteristic of Corymoiyha nutans^ 

 the only species of Corymorpha previously found at Plymouth. There 

 is also no indication that these gonophores could be transformed at a 

 later stage of their development into branched blastostyles. Besides, 

 they stand in their circle not singly and uniformly distributed, but 

 for the most part crowded near together in small groups. The 

 hydranth has eighteen aboral and sixteen oral tentacles ; but the 

 number of the aboral tentacles especially is still increasing, as is 

 shown by four very small tentacles, which I found in addition to 

 those enumerated above between the large ones. 



The hydranth is very sharply separated from the hydrocaulus. This 

 is not accurately represented in Hincks's JSgure, which shows incorrectly 



