256 TRANSACTIONS LIVEEPOOL, BIOLOGICAL SOCIETY. 



L. Agassiz {2) found in Massachusetts Bay a corymor- 

 pha-like hydroid budding off uni-tentacular medusae, to 

 which he gave the name Hybocodon prolifer. As Allman 

 (4) gives a description of the hydroid and medusa there is 

 no need to repeat all the details. The hydroid is about 2 

 inches long, about T V th of an inch in diameter below the 

 head, and thinner near the base. Perisarc smooth except 

 near the head where there are a few annular constrictions. 

 Coenosarc of the stem with longitudinal orange-red striae. 

 Hydranth with two verticils of tentacles, about sixteen 

 tentacles in each. The hydroid lives in rock-pools on 

 out-lying rocks away from the shore, about the Laminarian 

 Zone, usually three or four are together. 



Between the two verticils of the tentacles the medusa- 

 buds are situated just as in Corymorpha nutans. Medusas 

 are budded off from January to April. Agassiz apparently 

 has not seen any specimens of the adult medusas but 

 only those either upon the hydroid or just liberated, and 

 his description is confined to the earliest stage of the 

 medusa. The umbrella of the young medusa has the 

 margin obliquely cut off so that one side of the umbrella 

 is longer than the other. On the longest side of the 

 umbrella is situated a large tentacle-bulb carrying a soli- 

 tary tentacle, and also medusa-buds. There are three 

 other non-tentacular bulbs without tentacles in the usual 

 places upon the margin of the umbrella. The exumbrella 

 has five longitudinal rows of nematocysts which extend 

 from the margin to within a short distance of the apex of 

 the umbrella. One row is above each of the radial canals 

 running to the tentacle-bulbs not bearing tentacles, and 

 the other two rows are near the canal running to the 

 large tentacle-bulb. The rows of nematocysts are con- 

 spicuous early in the year by their orange-red colour, but 

 become inconspicuous about April. 



