56 BULLETIN OF THE 



tempt, and a short distance from the Morro light (] i miles), at a 

 depth varying from 242 to 42 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 a cursory examination, to consider the P. 

 Miilleri, 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 cin-i. 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 Eeef as well as of the Marquesas, with the 

 sections explaining their mode of fonnation. The weather during the 

 greater part of our trip from the Tortiigas to New Orleans was atrocious, 

 as is usually the case during March in the Gulf of Mexico. We man- 

 aged to do but little bej^ond 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 J 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. 



t RhizocrinuB has now been so carefully studied by Sars, by Pourtales, and by Ludwig, 

 that it will form an excellent standard of comparison for the other genera. 

 t Noticed in a general way in my first letter. 



