242 BULLETIN OF THE 



At Stockholm, Professor Loven permitted me to examine the whole of 

 that great collection, and Mr. Ljungman showed me the originals of his 

 O. rubra and 0. maculata. 



At Copenhagen, Dr. Liitken personally set hefore me the very rich collec- 

 tion of the University, and showed me the original of Wyville Thomson's 

 O, Liitkeni. I received like marks of kindness from Mr. Schmeltz of the 

 Museum Godeffroy at Hamburg ; from Professor Richiardi at Pisa ; Profes- 

 sor Panceri at Naples ; Sig. Trois at Venice ; Dr. von Martens at Berlin, 

 and from Professor Schlegel at Leyden.* 



All these Ophiothrices (with one exception presently to be mentioned) have 

 certain features in common. They have arms rather short, narrow, and 

 rounded, being from four to six times the diameter of the disk ; their lower 

 arm-plates have a notch or re-entering curve in their outer side ; the upper 

 arm-plates are more or less broad diamond-shaped or rhomboidal, and over- 

 lap one another. The arm-spines, eight or nine in number, stout, blunt, but 

 never club-ended, somewhat rounded, feebly translucent, the side thorns not 

 very distinct and from eleven to seventeen on each edge ; the disk beset with 

 grains, stumps, or short spines, except the radial shields, which are usually 

 naked, but sometimes have a few stumps which are merely the persistence of 

 a character of the young. 



Among these characters the plates of the arms furnish no clew whatsoever; 

 nor yet do the arm-spines, which present a wide range as to length, thickness, 

 and the number of thorns on their edges. A careful microscopic study of 

 the armature of the disk, its grains, stumps, or spines, is the best guide to 

 the specific differences ; to which may be added a consideration of the abso- 

 lute size attained by these specimens. Some hints, too, may be gained from 

 the pattern of color : but this must be taken with great caution. It is true 

 that writers, notably Grube, have successfully distinguished Ophiothrices 

 almost wholly by their coloration ; but this coloration is that which appears 

 after immersion in alcohol, and is not to be confounded with that of the living 

 animal. Thus Ophiothrix angulata has the most varied sets of hues,f but in 

 alcohol all these turn to pale blue. The pigment patches are arranged in 

 certain lines or patterns, which are brought out by the alcohol, and which 

 usually are characteristic. In this way, a stripe along the arm {0. Suensonii) 

 or regular spots on the disk (0. plana) are good guides to species. In the 

 European species this guide is often dubious, because many of the specimens, 



* To Professor Deshayes a special acknowledgment is due. Whenever I have 

 been in Paris he has taken me into his own laboratory at the Jardin des Plantes, 

 given me free access to the collections, and treated me, not as a stranger, but as 

 one who had a claim on his attention. 



t Illustrated Catalogue I., PI. II., Figs. 1, 2,3. 



