IV. New and Interesting Hydroids from Chesapeake Bay. 

 By Samuel F. Clarke, Ph.D., 



PROFESSOR OP NATURAL HISTORY, WILLIAMS COLLEGE ; DIRECTOR OP THE SUMMER SCHOOL OF ZOOLOGY OF 



THE JOHNS HOPKINS UNIVERSITY, 1881. 



Communicated Jan. 1'9, 1881. 



W HILE connected with the Chesapeake Zoological Laboratory in the summer of 1879 

 I had opportunities for studying some of the Hydroids of Chesapeake Bay. During the 

 early part of the summer we were stationed at Crisfield, Maryland, and later at Fort Wool, 

 Virginia. Again this summer I have had opportunities for work at Fort Wool and contin- 

 ued the studies begun there in 1879. My time was too limited to permit of more extended 

 work on the hydroids although there was a great supply of new and attractive material. 

 It will be noticed that all of the six forms described are of the gymnoblastic group ; all 

 but one are new species and for one of them a new genus has been established. 



The most interesting of the six forms is Stylactis arge, which has the remarkable habit 

 of dividing its hydranths by a transverse partition, leaving the distal half free, which latter 

 with its two or three hydrorhizal processes that are developed before the division takes 

 place, floats away free, being carried about by currents ; finally it settles down, becomes 

 attached and by growth and budding gives rise to a new colony. It is another method, in 

 which the hydroids are already so rich, by virtue of which they increase their numbers 

 and their geographical distribution. A second interesting feature of this species is the 

 fact that the gonophores in the female are quite highly developed, having radial and cir- 

 cular canals and may or may not become free. 



Calyptospadix is another interesting hydroid, especially in its hydrotheca-like processes 

 of perisarc, which are more like the genuine hydrothecae of the Calyptoblasts than any 

 thing else known among the Gymnoblastea. The species here described are 



Calyptospadix ceridea, gen. et sp. nov. 



Eudendrium cameum, sp. nov. 



Stylactis arge, sp. nov. 



Lovenella gracilis, sp. nov. 



Bougainvillia rugosa, sp. nov. 



Hydractinia echinata Fleming. 



