330 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



and pedigree of our cultures from which the urchins that he describes were obtained. 

 Some of these facts have been incorporated in the descriptions. 



In the following remarks about colours, it must be remembered that these vary- 

 within wide limits, and ai'e only given as approximate. It must also be remembered 

 that the exact outline and shape of the plates are somewhat difficult to settle from 

 the examination of living material alone. 



Description of Pure-hred and Hybrid Urchins. 



By Th. Moktensen, Copenhagen. 

 Echinus esculentus — 



The description is taken from a specimen raised from the egg in the laboratory, 

 which was barely a year old. 



Diameter of the test, 1"5 cm. ; height of test, 6 mm. 



Amhidacral plates, with a primary spine only on every second plate, this feature 

 appearing on the plates below the ambitus. On the aboral side sometimes three or 

 four successive plates have a primary spine, the alternation being thus less apparent. 

 The plates without a primary spine have a secondary one outside the series of 

 primary spines, near the tube-feet. At the ambitus the plates without primary 

 spines have, besides the spine near the tube-feet, another secondary one at the median 

 corner of the plate. The plates with primary spines have no secondary spines. The 

 number of ambulacral plates in each series is about eighteen. 



The interamhnlacral plates all carry a primary spine. At the fifth to sixth plate 

 from above two secondary spines make their appearance, one at the inner and another 

 at the outer upper edge. These spines are I'epeated on successive plates below the 

 ambitus, almost to the peristome. No other secondary spines are found. The 

 number of plates in each series is about twelve or thirteen. The spines are rather 

 robust and short, the longest being about 5 mm. in length. 



The apical plates have the shape typical of this species, all the ocular plates being 

 excluded from the periproct. The genital plates each carry a single spine at the 

 inner edge, except genital 5, which has two spines. The ocular plates have no 

 spines. The anal plates are rather conspicuous, the suranal plate being distinctly 

 larger than the adjoining plates. They do not carry spines. The genital openings 

 have not been formed. 



There are no spines on the buccal plates. The other plates of the buccal membrane 

 are not distinctly seen. 



The colour of the test is a violet-red, except the pore areas and the anal area, 

 which are nearly white. The spines are conspicuously violet, slightly banded with 

 white. The tip of the spines is white. The tube-feet of the aboral side have a slight 

 violet tint. 



