INTRODUCTORY. 



The collections of Hydroids obtained by Mr. de Pourtales during the ex- 

 ploration of the Gulf Stream between Florida and Cuba, while assistant 

 of the Coast Survey, were sent to me by Mr. Alexander Agassiz for deter- 

 mination. The collection, which had been put up in spirits and is, for the 

 most part, in an excellent state of preservation, proves to be a very large 

 one, and to contain a great number of undescribed sj^ecies. The determi- 

 nation of the specimens, and the drawing and description of the new 

 species, have occupied more time than I had anticipated, and with the 

 pressure of other avocations have caused more delay than I could have 

 wished in the publication of the results. 



All the enlarged drawings and details of structure have been carefully 

 made by myself, while most of the drawings representing the natural size 

 of the hydroid, as well as the completion of some of my sketches and the 

 drawing of the whole on stone, have been executed by Mr. Hollick ; and 

 I must here bear testimony to the truthfulness of his work and the almost 

 photographic actuality with which he has reproduced the natural form of 

 the specimen. 



One of the most striking features of the collection consists in the large 

 number of undescribed species, and the small percentage which can, with 

 probability, be referred to forms known to exist on the European side 

 of the Atlantic. 



Leaving out of consideration a few specimens whose characters, in con- 

 sequence of their imperfect preservation, could not be ascertained, the 

 collection consists of seventy-one species. Sixty-four are here figured and 

 described for the first time, and none of these have as yet been known to 

 occur beyond the area to which the exploration was confined. There thus 

 remain only seven species which, so far as their identification is possible, 



