56 BULLETIN OF THE 
tempt, and a short distance from the Morro light (14 miles), at a 
depth varying from 242 to 49 fathoms, he brought up no less than 
twenty perfect specimens of Pentacrinus * of all sizes, beside a, number 
of fragments which will be most useful for anatomical examination. 
The specimens obtained represent the two species thus far recognized, 
but I am inclined, from & cursory examination, to consider the P. 
Mülleri, with its distant cirri and more slender stem, merely as a 
younger stage of the P. Asterias, though the latter has a stouter stem 
and shorter intervals between the cirri. I shall send a number to 
Sir Wyville Thomson, who will examine our stalked Crinoids, Holo- 
pus and Pentacrinus,t at the same time with those of the “Chal- 
lenger," and who will thus have ample materials for comparison and 
description. While on the way from Key West to the Tortugas we 
stopped at the Marquesas Islands, which form a circular ring of islands. 
Their formation has undoubtedly been identical with that of the great 
Alacran Reef, briefly described in my first letter, and, from the fact 
that no corals are now found living on their weather side, these islands 
must have assumed their present shape at the time when their weather 
side made a part of the outer reef in connection with the islands of 
Key West and the other keys, previous to the formation of the present 
growing reef, or while the latter existed only in the shape of a submerged 
reef several fathoms below the surface. I shall, on another occasion, 
give maps of the Alacran Reef as well as of the Marquesas, with the 
sections explaining their mode of formation. The weather during the 
greater part of our trip from the Tortugas to New Orleans was atrocious, 
as is usually the case during March in the Gulf of Mexico. We man- 
aged to do but little beyond ascertaining, in the most general way, the 
faunal characteristics of the lines run between Key West and New 
Orleans. Our materials were, however, ample to show that the deep- 
water fauna on the western slope of the great Florida Bank corresponds 
with that of similar depths ¢ on the eastern slope of the Bank of Yuca- 
tan, and that this deep-water fauna extends over the bottom of the Gulf 
of Mexico, until the line running from the 100-fathom line in latitude 
of Tampa Bay towards New Orleans strikes the Mississippi River 
slope. Here, owing to the presence of dark, rich mud, the fauna 
materially changed its character, and we obtained, off the Passes of 
* See note from Captain Sigsbee. 
+ Rhizocrinus has now been so carefully studied by Sars, by Pourtalés, and by Ludwig, 
that it will form an excellent standard of comparison for the other genera. 
{ Noticed in a general way in my first letter. 
