26 DESMOSCYPHUS LONGITHECA. 



differs from this genus in the fact that the hydrothecae are also adnate 

 to one another in pairs, and thus brought all to one side of the hydro- 

 caulus ; while a still further difference is found in the fact that the inter- 

 nodes may in some cases carry each a single pair of hydrothecffi, as in Ser- 

 tularia. 



In the New Zealand species, Desmosci/phts BiisHi, the main stem is divided 

 into internodes of variable length, canying each a variable number of pairs 

 of hydrothecfB, while the branches are regularly divided into equal internodes 

 each with one pair of hydrothecae. In the species here described from the 

 Gulf Stream (Z>. longitheca), the entire hydrocaulus is regularly divided into 

 internodes, each carrying a single pair of hydrothecae. 



Desmoscyphus longitheca. 

 PI. XIV. Figs. 3-6. 



Trophosome. — Hydrocaulus attaining a height of about an inch, pinnately 

 branched ; pinnae alternate, much contracted at their origin ; main stem and 

 pinnsB divided into regular internodes, each internode carrying a single pair 

 of hydrothecaj. Hydrothecae long, tubular, with semicircular orifice, which 

 is closed by a valve-like lid ; along the branches and the greater part of 

 the main stem adnate to one another in pairs for nearly their entire height, 

 but becoming free and diverging from one another close to their distal ends; 

 towards the basal end of the stem the hydrothecae of each pair receding 

 from one another and ultimately disposed on two diametrically opposite 

 sides of the internode. 



Gonosome not known. 



Key West, shallow water. 



Desmoscyphus longitheca constitutes an interesting transition form by which 

 the genus Desmoscyphus becomes connected with Sertularia. For while in 

 D. Buskii the branches alone are divided into equal internodes, each carry- 

 ing a single pair of hydrothecfe, the main stem being composed of internodes 

 of variable length, each with a variable number of hydrothecae, in the present 

 species both stem and branches possess the Sertularian character of division 

 into equal internodes, with a single pair of hydrothecfe upon each. 



Further, in D. longitheca the hydrothecfB composing each pair, where they 

 approach the base of the main stem, begin to recede from one another, the 

 separation gradually increasing, until just above the hydrorhiza they are 

 situated upon opposite sides of their supporting internode exactly as in a 



