210 Mr. R. Kiikpatrick on Ilexactinallid 



diasters, &c. Accordingly I suggest the terms Holactine * 

 and Astral. 



Holactine spicules have only actines. Astral spicules have 

 end spines or distal appendages at the ends of the actines. 



Notes on some of the above terms. 



(1) Since there are no known hemipentasters &c, and, of 

 course, no holopentasters &c, the prefix " mono- " is not 

 required before " stauraster," " diaster," &c. 



(2) Stauractin is used for spicules with four actines in one 

 plane, and tetractin for spicules with rays forming a pyramid 

 as in Aulorossella longstaffi, Kirkp. 



(3) The correct designation for the spicule for which I 

 suggested the name monoxyhexaster in the " Report on the 

 * Discovery ' Hexactinellida," p. 3, footnote, has been the 

 subject of controversy. The term was proposed for hexasters 

 with only one end-spine to each actine. Ijima (Oontiib. ii. 

 p. 10, and iii. p. 118) called these spicules hexactinose hex- 

 asters, and " monoxyhexaster " was suggested by me as a 

 convenient single word. Schulze (Abband. Akad. Wiss. 

 Berlin, 1903, p. 8) prefers the " actin " to the " aster " suffix, 

 and in Prelim. Rep. ' Gauss' Hexactinellida (Zool. Anzeig. 

 Jan. 4, 1910, p. 296) he uses the terms heterohexactin &c. 

 In my opinion the use of such a term gives an undue im- 

 portance to the question of the number of the end-spines. 



The spicule which I term monohexaster is one with a 

 centrifugal end-spine or distal appendage at the end of each 

 actine, and therefore it must be grouped with the Astral 

 group of hexasters with centrifugal end-spines, and not with 

 the hexactin?, in which the actines are wholly without end- 

 spines or distal appendages. The relative unimportance of 

 the mere number of spines is seen in the endless variation 

 of these structures not merely in different spicules, but even 

 in one and the same spicule (as in hemihexasters, hemi- 

 calycocomes, &c ) . In my opinion the presence or absence 

 of end-spines is the all-important point. If end-spines are 

 absent the spicule is an " actin " spicule, if present an " aster " 

 spicule. 



The solid appendages at the ends of the (cored) actines of 

 spicules of the Astral group are probably merely spines like 

 the Stitenstachein, as Schulze has already pointed out (Phys. 

 Abhand. Akad. Wiss. Berlin, 1886, p. 15). 



The variation in number &c. of end-spines is indicated by 

 the prefixes holo-, hemi-, mono-. Strictly I should have 



* 6'Aor, sole or solely. 



