The Aftiniae of the Plate Collectioii. 261 



tliroug'h the Perforation. A long-itudinal fluting* is iioticeable in 

 most of tlie specimens. The tentacles of the innermost eycle take 

 their origin directly from the disc, but tliose of the second cycle 

 arise from the siinimit of radial ridges which gradually increase in 

 heiglit as they are traced peripherally, and the outer cycles arise 

 from other ridges, each of which as it is traced peripherall}^ becomes 

 confluent with the adjacent ridge of the tentacle of the next oldest 

 cycle. It is thus possible to separate the tentacles into gronps, eacli 

 of which Clusters, as it were, around a ridge bearing a tentacle of 

 the second cycle, the lines separating adjacent groups passing 

 tliiough tentacles of the innermost cycle. 



The disc is somewhat concave and is marked by radiating 

 grooves separating areas which are coutinuous peripherally with 

 the ridges bearing the second cycle tentacles. The peristome is 

 somewhat elevated and the stomatodaeum is longitudinally ridged 

 and provided with two siphonoglyphs. 



The measurements diifer in difterent individuals somewhat, in 

 accordance with the form assumed in contraction. The majority of 

 the specimens are cousiderably broader tlian high and are somewhat 

 smaller in diameter at the base than they are at the margin. 

 Measurements of three individuals of this form gave for the height 

 3 cm, 3 cm and 3.7 cm, for the diameter at the base 3 cm, 3.5 cm 

 and 3 cm, for the diameter at the broadest part ot the column ö.5 cm, 

 4.7 cm, and 5 cm. Other individuals are higher in proportion to 

 the diameter and have a more conical form, and measurements of 

 three of there gave for the height 4.5 cm, 3.0 cm, and 4.0 cm, for 

 the diameter of the base 3.7 cm, 3.0 cm, and 3.4 cm, and for the dia- 

 meter of the margin or rather of the column just below the margin 

 3.0 cm, 2.2 cm, and 2.5 cm. The tentacles vary in dififerent individuals 

 from 0.4 cm to 0.6 cm in length, according to the degree of contraction. 



The great majority of the specimens in their preserved conditiou 

 are of an olive-green coloi". The base and stomatodaeum are paler 

 and rather brownish or flesh-colored, and the tentacles and disc are 

 usually somewhat darker than the column. The acrorhagi are, as 

 a rule, pal er than the column tubercles, a condition which agrees 

 with what might be expected from Drayton's descriptions of their 

 coloration. Two specimens from Cavancha (No. 18), however, had a 

 ditferent color from the majority, being of a uniform pale brown,. 

 and the Single specimen from Iquique is, so far as its ectoderm is 

 concerned, quite colorless, pigment in the endoderm, however, giving 



