36 PHORMOSOMA URANUS. 



structural feature of P. uranus consists 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 Phormosoma and Calveria." While this is 

 true 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 band 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. uranus 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. uranus intermediate in size between the smaller specimen described 

 1)\ 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. Peterm. 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 surface 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 Uesml. 



Florida, West India Islands. Littoral to 250 fathom 



Strongylocentrotus Drobachiensis A. Ao. 

 (Eaat Coast of United States,) Lat. 41° 30* N., Long. 66' W , in ::'. fathoms. 



