36 PHORMOSOMA URANUS. 
structural feature of P. vranm cousists in the extreme tenuity of the test, 
and in the fact that " there is but little difference in character between 
the upper and lower surfaces of the test, and the species thus holds a place 
intermediate between the genera Phormosoraa and Calveria." While this is 
time of specimens of the size of that figured by Thomson, and of younger 
ones, it does not hold good for larger specimens, in which we find that 
the larger tubercles of the actinal surface are comparatively small, and not 
limited to a narrow bnnd of the actinal and abactinal surfaces immediately 
adjoining the ambitus. But, on the contrary, in older and larger speci- 
mens the primary tubercles of the actinal surface become larger with age, 
extending at the same time over a greater portion of the actinal surface 
from the ambitus towards the actinostome, as in other species of the genus 
Phormosoma. Of P. iiranns I had on former occasions only the opportunity 
of examining the very imperfect specimen described by Thomson. Since 
that time Mr. Murray has sent me for examination the Echini collected by 
the Knight- Errant in the Faroe Channel. Among them was a specimen 
of P. Iiranns intermediate in size between the smaller specimen described 
by Thomson and the larger and older specimens collected by the Blake 
from the West Indies and off the southern part of the Atlantic coast of 
the United States, which I had named P. Petersii. A renewed comparison 
of the specimens with this additional material plainly shows that the differ- 
ences which had been noticed between them were merely due to age, and 
that in this species the great development of the large primary tubercles 
of the actinal surfixce takes place at a late period of growth. The abactinal 
system also seems to increase more rapidly in size in proportion to the rest 
of the test, as the specimens grow larger ; so that in younger specimens 
the abactinal system is relatively smaller compared with the diameter of the 
test than in the larger ones. The specimens collected were all of a brilliant 
claret-color. 
Echinometra subangularis Desml. 
Florida, West India Islands. Littoral to 250 fathoms. 
I 
Strongylocentrotus Drbbachiensis A. Ag. 
(East Coast of United States,) Lat. 41° 30' N., Long. C6° W., in 73 fathoms. 
