﻿56 



PROCEEDINGS OF THE 



[Dec, 1856. 



In the summer of 1856, I had myself the good fortune to meet 

 with, and follow out more in detail a mode of embryonic develop- 

 ment on the whole entirely analogous to the preceding, though 

 differing from them in some points. But what is most surprising 

 is the fact that the Medusa on which these observations were 

 made, was not a member of the iEginide family, but belonged to 

 the highest group of the Naked-eyed Medusae, that of Oceanidae. 



On the 10th of June, of the past summer (1856,) I first took with 

 the dip-net a small Medusa, closely allied to Turris in appearance. 

 Its relations to Oceania were not less striking but still there are 

 points of structure which appear to distinguish it from either. 

 Most of these specimens were about the tenth of an inch in height, 

 but one of them was of still less size, and about a month afterwards 

 I took together quite a number of specimens rather more than 

 double the size of those first found, and which I afterwards ascer- 

 tained were full grown individuals. The smallest size was never 

 met with afterwards. — But three larger sizes continued to be found 

 from time to time until the early part of October. (Oct. 4.) 



This is an animal of rare beauty which my inexperienced pencil 

 has attempted to give some faint idea of in PL 4. ff. 1 & 2. etc. I 

 regret the circumstance that no artist could be procured at the time 

 to do it justice. 



The principal difference between the genera Oceania and Turris, 

 as defined by Prof. Ed. Forbes, is the presence in the latter of dis- 

 tinct longitudinal muscular bands, four in number, which alternate 

 with the four vertical chymiferous tubes. Both of these genera, as 

 well as Saphenia, are represented by that eminent naturalist, as 

 possessing regularly and beautifully convoluted sexual organs. I 

 have to mention, at once, that neither in the present Medusa, nor 

 in a beautiful Saphenia, also taken by me in our harbor, have 1 

 found any appearance confirming this observation. 



The present sub-genus, for which I propose the name Turritop- 

 sis, is distinguished from Turris by the following peculiarities. 

 The swimbell is remarkably thin, having no accumulation of trans- 

 parent tissue above as in Oceania and Turris, but the whole 

 appears to be a muscular mass covered by epithelium within and 

 without. The vertical muscular bands are replaced by a single 

 line or seam which does not reach the marginal tube; the tentacula, 

 which, as in Turris, are very numerous and solid, have an elonga- 

 ted bulb at base, on the inner surface of which is an eye-speck 

 composed of a constellation of pigment spots. (PL 4, fig. 9.) The 



