ECHINOTHURID^. 33 



and Astlienosoina cannot be distingui.shud, he tlien establishes a number of 

 new genera based wholly upon the structure of the triphyllous and tridentate 

 pedicellarias.* The latter show " a great variety of forms, and are of great 

 systematic importance ; " while the former have little systematic importance 

 in Echinidoe, they are considered by Dr. Mortensen of value for the determi- 

 nation of the Echinothuria3. 



Dr. Mortensen has given a number of plates of most admirably drawn 

 pedicellariae and colored figures of several species of Echinoids. He is 

 most outspoken regarding the quahty of the illustrations of many of his 

 predecessors. Surely we might call his attention to a number of figures on 

 Plates IV, V, VI, VII, XV of the ''Ingolf " Echinoidea, and refer them to his 

 benevolent criticisms. When such minute characters as those of pedicel- 

 lariae are to be illustrated, it is important that we should know their size 

 and kind, but in a great many of his figures the explanation of the plates 

 gives us no information on the subject. Surely he cannot expect his 

 readers to calculate the enlargement of his figures from the data of the 

 oculars and objectives used in drawing them. 



It seems rather hazardous to state, as is done by Dr. Mortensen, that the 

 tetradactyle pedicellariae described by Thomson for Asthenosoma fenestrata are 

 only found in the two species for which he has established the genus Araeo- 

 soma.^ No one who has dredged EchinothuriaD from great depths can have 

 failed to notice how frequently the tests come up more or less injured, with 

 their appendages completely worn off. Should the same tetradactyle pedi- 

 cellariae be found in other Echinothuriae they would, according to Dr. 

 Mortensen, have to be referred to the genus Araeosoma, even if the triden- 

 tate pedicellariae were different; for certainly the differences in the triden- 

 tate pedicellariae of Asthenosoma fenestrata and o^ Asthenosoma hystrix, figured 

 by Dr. Mortensen (PI. XIV, figs. 8, 17, 18, 21, 32, and PI. XIII, figs. 17, 

 18, PI. XIV, fig. 26) cannot be regarded as sufficient to separate diem 

 generically. 



Ophicephalous pedicellariae occur not only in Tromikosoma Koehkri 

 (Mortensen, PL XIV, figs. 19, 23), but also in Phonnosoma lucidentum (I have 

 figured them, " Challenger" Echinoidea, PL XLIV, fig. 27). Dr. Mortensen 

 refers that species with some hesitation to his genus Hygrosoma on account of 

 the thick broad blades of a peculiar kind of tridentate pedicellaria3 (Mortensen, 

 PL XIII, fig. 16). I take it they are the pedicellariae of which I have given 



1 Mortensen, 1. c. p. 9. ' Mortensen, I. c. p. 53. 



