224 BULLETIN OF THE 



HYDROIDA. 



Sarsia mirabilis. Ag. 



Many specimens of Sarsia were seen at Grand Manan on a single excursion. 

 Later they disappeared, and were not again collected. The hydroid Coryne * 

 was also found. 



Hydrichthys mirus, gen. et sp. nov. 



Plates IV., V. 



During the month of August of the past summer (1887), in the surface 

 fishing carried on at the Newport Marine Laboratory, I captured a most inter- 

 esting genus of parasitic hydroid. This genus and its peculiar life are un- 

 described as far as known. The mode of parasitic life is most extraordinary, 

 and the modification of its structure of an anomalous character. 



A small fish of the genus Seriola (S. zonata, Cuv.) was taken in the dip- 

 net at a time when the sea was quiet.f Upon the side of the body (Plate IV. 



primitive medusa, the ancestral form of the medusae, with the prototype ("Pili- 

 dium-like larva ") of the six groups of marine larvse described by Balfour. It is 

 thought that such a resemblance not only exists, but also has an important phylo- 

 genetic meaning. It is not in place to discuss this question in this paper. 



It may be asked whether the primitive larva of Agalma, with its huge primitive 

 covering scale, or the primitive larva of Nanomia, where that scale is replaced by 

 a float, is nearest the primary or ancestral larva of Hydromedusae. The youngest 

 forms of the primitive covering scale and the float closelj' resemble each other, 

 and the departure from that form seems greater in Agalma than in Nanomia. A 

 nectocalyx seems more highly organized than a pneumatophore ; still, between a 

 primitive hydrophyllium, such as exists in Agalma, and a float like that of Nano- 

 mia, it is hard to tell which is more highly specialized. It cannot be said that the 

 adult Nanomia is less highly specialized than the adult Agalma. Although the float 

 of Nanomia is first formed, it follows the primitive hydrophyllium in Agalma. 

 While this fact might seem to indicate want of homology of the float in the adults 

 of the two genera, it does not seem to prevent our considering the primitive larva 

 to be represented by the young Nanomia with a float and no covering scale. 



* Although it was not my intention to speak of the hydroids collected in tne 

 Bay of Fundy, I must mention beautiful specimens of Corymorpha dredged in 

 shallow water not far from Eastport. The medusae were just ready to drop from 

 the hydroids, and as they were almost mature in July probably in later months 

 they are found in abundance free swimming in the sea. I was of course on the 

 look-out for the so-called free liydroid Acaulis, Stimpson, and other similar hy- 

 droids, but was unable to collect any of these animals. The broken heads of tlie 

 liydroid Pennaria, which somewhat resemble Acaulis, were found. 



t The Seriola was in company with two others. Neither of its companions, 

 however, were afHicted with the paVasites mentioned below. 



