REPORT ON THE ECHINOIDEA—MORTENSEN 3 
comparison with the West Indian seas, from which we know alto- 
gether only five species, shows strikingly that in regard to the 
echinothurids, as with the cidarids, the Malayan region is extraor- 
dinarily rich, probably the richest in the world. 
With regard to the saleniids there is no such preponderance, the 
few surviving representatives of this formerly so flourishing group 
being about equally richly—or poorly—represented in the Indo- 
Pacific and Atlantic areas. 
Of the arbaciids, the few small deep-sea forms known are rather 
equally distributed, like the saleniids. But out of the nine species 
of the large and splendid Coelopleurus type, the Malayan region 
with four species as contrasted with only one in the West Indies 
stands as the richest region. As a small compensation for this rela- 
tive poverty of the Atlantic area stands the fact that the genus 
Arbacia is confined exclusively to the Atlantic region and the west 
coast of America, no representative of this genus, or of the related 
genus Tetrapygus, being found anywhere in the Indo-Pacific region. 
Statements in the older literature of the occurrence of species of 
Arbacia or of Tetrapygus in the Indo-Pacific, as for instance at 
Zamboanga, are all erroneous, based wpon old and unreliable labels. 
Also in the material sent me from the United States National Museum 
there is a specimen of Tetrapygus niger labeled “Philippines; G. B. 
Steere; Acc. No. 39067.” That the label is wrong is beyond doubt. 
I am under the greatest obligation to Dr. Alexander Wetmore, in 
charge of the National Museum, for permitting me to include in volume 
2 of my Monograph of the Echinoidea descriptions and illustrations 
of various new forms in the families herein dealt with that were 
found in the Albatross collection. If I had had to wait for the publi- 
cation of this part of the Albatross report before I could deal with 
these forms in the Monograph, it would have delayed the publication 
of the Monograph very considerably. From a scientific point of view 
also it is more satisfactory to have the full descriptions and the fig- 
ures of the various new forms from the Albatross collection in the 
right systematic place in the Monograph, instead of mere references 
to the Albatross report. Now I may in the main restrict the mention 
of the new forms in the Albatross report to references to the 
Monograph. 
It may be taken as a matter of course that all the material repre- 
senting already known species contained in the Albatross collection 
has been made use of in working out that Monograph, it being of the 
greatest importance to have that work based upon as extensive ma- 
terial as possible. 
