H4 



CHAS. W. HARGITT. 



Pasythea. — Among hydroids obtained from the gulf-weed 

 were found extensive colonies of what seems clearly to be a 

 species of Pasythea, a genus hitherto unrecorded anywhere 

 within our northeastern Atlantic coast region. Indeed only a 

 single species of this genus is recorded from American waters 

 (Nutting, "American Hydroids," Part II., p. 75), namely P. 

 quadridentata Lamx., specimens of which he reports from the 

 British West Indies. From a careful comparison of Nutting's 

 figures and description, as well as those of Lam- 

 arck, Lendenfeld, and others, my specimens seem 

 to have so many points of difference as to suggest 

 the probability of their being undescribed. Hence 

 it seems important that a rather full description be 

 undertaken, which is given below. 



Trophosome : Colony consisting usually of a 

 simple unbranched stem, varying in height from 4 

 to 9 mm., or averaging about 6 or 7 mm., and ris- 

 ing from a creeping hydrorhiza which forms an 

 intricate network over the stems and leaves of the 

 alga. The stem .is divided into a series of inter- 

 nodes by oblique nodal articulations, as shown in 

 Fig. 13. Each of these internodal segments bears 

 from one to five pairs of opposite, and closely 

 appressed, hydrothecae, the mouths of which are 

 quite divergent as shown in the figures, especially 

 in internodes having several pairs, the terminal pair 

 of which in such cases are much less so, owing no 

 doubt to the absence of pressure from above. The 

 number of internodes varies greatly on different 

 stems, as is shown in the accompanying table* The 

 average, estimated from a series taken more or less 

 at random, seems to be about five, though this is 

 probably somewhat dependent upon age or con- 

 ditions of growth. Furthermore, the size of internodes is like- 

 wise variable, even more than their number. This is largely a 

 matter of the number of hydrothecae upon a given internode. 

 A glance at the table, and a comparison of the figures, will make 

 this quite obvious without extended verbal description. Usually 



Fig. 13. 



