vol.].] Torre y . — Hydroida of the Pari fie Const. 65 



between tides. Monterey, San Francisco, and Tomales Pt. 

 ( Trask ) . San Diego, Santa Cruz, Cal. , and Vancouver I ( ( 'lark ) . 

 Bare I. (Hartlaub). Townsend Harbor, 15-20 fathoms (8. 

 conica and 8. nodulosa Calkins.) 



The figures on Pis. VII and VIII show at a glance the unusual 

 variability of this species. Trask's type came from San Francisco 

 Bay, and it is from colonics from San Francisco Entrance that 

 Figs. 59, 60, and (il have been drawn. Figs. 59 and 60 represent 

 the two types of gonothecae described by Clark, the first approach- 

 ing the gonotheca of 8. polyzowias. Figs. (i'J and 63 were drawn 

 from the same colony from San Pedro, and mark stages in the 

 transition from the unriaged spinj type through a ringed spiny 

 condition to the form typical of S. polyzonias, reached in colonies 

 from San Diego (Fig. 68). As a rule the hydrothecae on colonies 

 with aunulated gonothecae are transversely ridged or annulated, 

 and somewhat narrowed distally. The length and diameter of the 

 intcrnodes and the degree of immersion of the hydrothecae in the 

 stem vary considerably. 



In spite of the wide range of variation, there are always three 

 teeth on the margin of each hydrotheca, the proportions are in 

 general constant, and the stems are stiff, flexuous and sparely 

 branched. 



The causes of the variation are not clear. Trask's type grows 

 on the shore rocks, between tides, from Tomales Pt. to Pacific 

 Grove. The synonymous 8. nodulosa Calkins, dredged at 15-20 

 fathoms in Townsend Harbor, Wash., is also found in 9 fathoms 

 near San Pedro, Cal. Only the dredged forms seem to be tran- 

 seversely wrinkled. It is impossible to estimate the value of 

 these and similar facts, however, without the aid of experimenta- 

 tion. 



Dynamena group. 



Hydrothecae opposite, a joint between each pair. 



Sertularia desmoidis, sp. nov. 



PI. VIII. Figs. 70, 71, 7J. 



Trophosome. Stems rising from a creeping stolon to the height of one to 



two inches, branching sparely and irregularly, forming at times a matted 



tangle with bryozoa. Internodes vary somewhat in length; the portion distal 



to tin- hydrothecae is never longer than the rest of the internode. On the 



