336 MESSES. C. SHEAREK, W. DE MORGAN, AND H. M. FUCHS 



K = E. miliaris ^ X E. acutus $ , fertilized 6.5.12. — 



Total . . 5 ,, 



All urchins had paternal tube-feet character. 

 Young urchins from B and K were placed together. 

 Diameter of test, 2 cm. Height, 1 cm. 



The ambulacral 2)lates all carry a primary spine. The upper plates possess no 

 other spines ; from the sixth to the seventh there is a secondary one at the inner 

 upper edge of the plate. The number of ambulacral plates in each series is about 

 eighteen. 



The interavibulacral plates likewise all carry a primary spine. The secondary 

 spines are very few. On the third to the fo\irth plate from the top there is a 

 secondary spine at the upper outer and inner edge of the plate, and this is repeated 

 on each successive plate down below the ambitus. Likewise on the sixth to the 

 seventh plate there is one at the inner median corner and one at the middle of the 

 outer edge which is repeated on successive plates downwards. The number of 

 interambulacral plates in each series is about thirteen. The length of the primary 

 spines is about 5 mm. 



The limits of the apical plates are hard to distinguish. The ociilar plates are all 

 certainly excluded from the periproct. The genital plates each carry two small 

 spines. The ocular plates each carry one. The anal plates are rather large, and the 

 central (suranal) plate is scarcely larger than the adjoining plates. There is a small 

 spine on each of the larger anal plates. The genital pores have not formed. 



On the buccal membrane there are some small thin but distinct plates which do 

 not lie very close together. There are no spines on the buccal plates. 



The colour of the test is not so pronounced as in the pure-bred E. miliaris of the 

 same size. There is a dark greenish tint on the median line of each series of plates, 

 the outer and inner portion remaining more or less white. On each apical plate 

 there is a green spot. The spines are greenish at the base, assuming a pinkish tint 

 towards the tip. The secondary spines are white at the tip. The tube-feet are pink, 

 the colour being arranged in rings on those of the oral surface. 



The pedicellarifB. While the ophicephalous pedicellarise present no features worthy 

 of special interest, as might be expected from the fact that in both parent species 

 they are very much alike, the other pedicellariee present some characters of 

 importance. The tridentate pedicellarise are long and slender as in E. acutus, and 



