No. 5.— Reports on the Dredging Operations off the West Coast 
of Central America to the Galapagos, to the West Coast of 
Mexico, and in the Gulf of California, in charge of ALEXANDER 
Acassiz, carried on by the U. S. Fish Commission Steamer 
« Albatross,” during 1891, LizuT. CoMMANDER Z. L. TANNER, 
U.S. N., Commanding. 
XXIII. 
Preliminary Report on the Echini. By ALEXANDER AGASSIZ. 
Tue following brief descriptions, accompanied with figures of the 
more interesting species, collected during the ‘ Albatross ” Expedition 
of 1891, are published to prevent possible confusion in the names 
adopted for the new species of sea-urchins, which will appear on the 
Plates preparing for the final Report. 
As regards the distribution of Echini in the Pacific, we have at the 
present day a condition of things very similar to that which must have 
prevailed in the Atlantic when the species of Echini living in the Crag 
and in the Maltese beds had their representatives in the West Indies, 
having, as has been suggested, found their way from the Mediterranean 
along the shores of an ancient continent. Some of the species living 
on the west coast of Central America have a very extended geographi- 
cal distribution in the Pacific, and yet no one claims that this great 
range has been brought about by their migration along the shores 
of a continent, or continental islands, existing between Panama and 
the Sandwich Islands or the Marquesas. 
The great equatorial current gives us a cause fully efficient to effect 
such a wide distribution, and that in a comparatively short time. While 
undoubtedly many of the species of Echini have no pelagic Plutei, and 
are so to speak viviparous, or carry their young for a considerable period, 
yet we should remember that young Echini, even after they have 
assumed the characters of the adult, are capable of being transported 
VOL. XXXII. — NO. 6. 1 
