Notes on some Hydromedusae from the Bay of Naples. 575 



iMAN the habitat varies from tide pools to considerahle depths, and 

 on fragments of rocks, shells, etc. 



While eonforming iu inost respects to the diagnoses given of 

 the species by Hincks and Allman (op. cit.) iu some few points 

 there are differences, though not to my mind of any conslderable 

 importauce. As to size Hincks gives the height of the hydroid as 

 from 12 to 20 mm, while according to Allman it averages about 

 6 mm. In my own specimens the height varied from 3 to 6 mm in 

 the expanded condition. It would seem that Hincks must have 

 had very unusual specimens, or that in some way his figures are 

 incorrect. 



A point of most difference is that concerning the location of 

 the gonophores on the hydranth. According to hoth the previously 

 named observers these bodies arise low upon the body of the hy- 

 dranth and in a single, or sub-verticillate Cluster. I have found 

 them arising in severa! Clusters or even singly, at any point or 

 portion of the hydranth, and quite as frequently near the orai as 

 the basai region of the body. They are home on short pedieels, 

 frequently in Clusters of from two to four on the same peduncle. 



The Medusa. At birth the medusae are sub-spherical and 

 average about 0.6 mm in diameter, and have two well developed ten- 

 tacles, which arise from large bulbous bases on opposite sides of 

 the body, each tentacle provided with numerous stalked nematocysts. 

 As noticed in a previous paragraph, they live well in the aquarium, 

 but do not appear to grow to any appreciable extent. The largest 

 specimen measured 0.8 mm in height by 0.7 mm in breadth. The 

 general aspects of the little creature are shown in fig. 29, but no 

 figure can delineate the elegant grace and beauty which it exhibits 

 when floating languidly with tentacles extended, like delicate strea- 

 mers fringed with an exquisite embroidery of stalked batteries of 

 nematocysts, to a length of ten times the diameter of the beli, or 

 quivers in magic undulations as the limpid creature pulses itself 

 through the water. Little wonder is it that, observing something 

 of its exquisite features that prince of earlier observers, McCkady, 

 as expressing his sense of the beautiful, ascribed to the genus the 

 name Gemmaria^ the little gem! 



As Allman has well remarked, one of the most unique among 

 the several characters of this medusa is that of the numerous, stalked 

 capsules of nematocysts which fringe the tentacles. From near the 

 basai bulbs to their very tips, the tentacles are irregularly covered 



38* 



