94 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



equal and grooved, the distribution of the syzygies is quite different on the pos- 

 terior arms. 



In the species of Comasteridse possessing grooveless arms it is usually only the 

 two posterior rays which carry them, but in large species with very numerous arms 

 a number may be found on each ray. In Comanthus parvicirra from the Philip- 

 pine Islands Carpenter found that the distribution of the ungrooved arms, as well 

 as their number, varies to a very great extent. He notes that in any case they 

 always occur on the odd (left) posterior radius, D; when more are developed they 

 may occur on the posterior divisions, C 2 and Ej of the two lateral radii, C and E ; 



and when the proportion of 

 nontentaculiferous to tenta- 

 culiferous arms becomes very 

 great, more or fewer of the 

 anterolateral arms C, and E 2 

 belong to the former class, 

 while in exceptional cases 

 nontentaculiferous arms may 

 even occur on the anterior 

 radii. 



In only one individual 

 did Carpenter find a nonten- 

 taculiferous arm on one of 

 the two anterior radii. In 

 this specimen out of 31 arms 

 19 were entirely devoid of a 

 tentacular apparatus, and in 

 15 of these the fusion of the 

 two sides of the ambulacral 

 grooves had taken place either 

 on the disk or on the proximal 

 brachials, so that an ambu- 

 lacral nerve was wanting in 

 nearly half of the total num- 



FIQ. 181. CENTRAL PORTION AND ONE POST-RADIAL SERIES OF SPECI- ber of arms. In the other 

 MEN OF CAPILLASTER MCLTIRADIATA MO,, " ALBATROSS STATION four nonten taCuliferOUS arms 



the groove remained open for 



a short distance and then closed in the usual manner. Three of these four arms 

 constituted the anterior division (E 2 ) of the left lateral ambulacrum, but the fourth 

 was the first arm of the left anterior ambulacrum, and was borne upon the same 

 IIIBr axillary as a well- developed ordinary tentaculiferous arm. 



In some specimens of Comanthus parvicirra Carpenter found that the arms 

 are all alike in possessing open ambulacral grooves fringed with crescentic lappets 

 and groups of tentacles. 



In Comatula Solaris he found that the arms may be all grooved, or anywhere 

 from one to four may be nontentaculiferous. 



181 



