ECHINODEKM LARVM. 469 



recorded tlie occurrence of Echinoderm larvae in the 

 plankton around the south end of the Isle of Man, and 

 their relative number on one occasion is stated; but no 

 attempt is made to name them nor to refer them to their 

 respective orders, as the object of their investigation was 

 to determine the statistics of groups rather than to 

 identify the species. I venture, therefore, to hope that 

 the present contribution to an exact knowledge of these 

 interesting larvae as they occur in the above-named area 

 may be found useful by future workers in the same field. 

 It may be of interest, to give some idea of the number 

 of Echinoderm larvae which may occur at times, to quote 

 the following sentences from the Twenty-second Annual 

 Report of the Lancashire Sea-Fisheries Laboratory (8), 

 p. 292 : — " Echinoderm larvae were unusually abundant 

 in 1918. Absent in January, they appeared suddenly in 

 our nets on February 6th, to the number of 3,040, and 

 attained their maximum of 51,200 as early as February 

 13th. Other large hauls were 24,080 (February 20th), 

 17,000 (February 27th), 24,360 (March 10th), and 

 27,150 (March 13th). The numbers dropped to zero by 

 the middle of April, but Echinoderm larvae were present 

 occasionally from this time on to the end of October, and 

 on July 17th there was a large haul of 30,000. Twice in 

 September the numbers reached the thousands (7,400 on 

 the 11th, and 4,000 on the 18th)." These figures repre- 

 sent the number present in the official hauls across Port 

 Erin Bay. The large numbers stated as having occurred 

 in February and March refer to the as yet unidentified 

 spatangoid pluteus shown in figs. 61-64, PL IX, and the 

 ophiopluteus shown in fig. 37, PL VI. The former was 

 much the more numerous. A few bipinnariae of Aster i as 

 rubens may be included; but, compared with the 

 spatangoid pluteus, the number was in significant. 



