PENNARIA PACIFICA. 7 



numerous, three to seven usually, on each internode of the stem, some- 

 times nine, not in the form of simple rings, but saucer-shaped (see PI. 2, 

 fig. S), five to seven at the base of each pinna, and the same number at the 

 base of each peduncle. The annular base of the peduncle is the narrowest 

 part and is much compressed, making one of its transverse diameters much 

 greater than the other. The hydranths are not very well preserved in 

 either lot of specimens, and I discover no marked differences in those of 

 equal size like the ones in terminal positions on the main stem and pinnae. 

 As the stem and pinnae elongate, a new hydranth is formed just below the 

 terminal, and as the terminal hydranth is the largest on the pinna, the 

 largest and oldest is always next to the youngest and smallest, however 

 many there may be on the pinna. 



It is possible that when we have more material with the gonosomes of 

 both these species, and we know their complete life histories, we can unite 

 the two. 



I have had an opportunity to study the original specimens of Pennaria 

 gibbosa L. Agassiz from Key West. In studying P. symmetrica for description 

 I considered it distinct from P. gibbosa, because of the gibbous shape of the 

 hydranth, and the very slender, tapering, completely annulated character of 

 the peduncle showing no compression at the base, in the description of 

 gibbosa. In comparing the specimens of the two 1 find that the peduncles 

 are alike in both and the hydranths of one are as gibbous as those of the 

 the other (see PI. 2, figs. 2 and 4). The filiform tentacles are somewhat 

 longer in symmetrica than in gibbosa, but that is a feature of slight value. 

 Pennaria symmetrica Clarke becomes a synonym of Pennaria gibbosa Agassiz. 



A fact of some importance in valuing the characters of the species of 

 Pennaria is found in the changes produced by somewhat different environ- 

 ment even in localities close together. In examining specimens of Pen- 

 naria tiarella from Woods Hole, Mass., I was impressed with the differences 

 between the specimens from the piles of the wharf and those growing on 

 the long, slender, ribbon-like leaves of eelgrass (Zostera) near-by. Those 

 from the eelg-rass have stems much smaller at the base than at the distal 

 ends, the latter often being twice the diameter of the basal part. (See 

 PI. 3, figs. 3, j t ). In the specimens from the wharf the base of the stem is 

 but slightly smaller than the distal end ; the difference is obvious in one, 

 while in the other it would not be seen without careful observation (see 

 PI 3 7 figs. 1, 2). The basal third or two thirds of the stem, in the specimens 



