Mr. Jeffreys on the Comparative Size of Marine MoUusca. 197 



rangial sacs, with their parent-joints still attached, are constantly 

 to be met with, placed side by side, and probably retained near 

 each other by a common mucous envelope. The cells at this 

 period are elliptical, their ends being produced somewhat, and 

 coalescing with the now empty joints. At maturity, the old 

 joints are cast off entirely, the cell closes, assumes a perfectly 

 elHptical outline, and the sporangium presents itself in a guise 

 similar to the mature detached sporangia seen in some of the 

 Zygnemacese. 



The mucous matrix in which the species of this genus are 

 imbedded often exhibits a number of pin-like bodies, stuck, as it 

 were, into every part of the joint, — the heads, which are minute, 

 oblong, granular, and of a rich green colour, being directed out- 

 wards. These growths appear to be epiphytical, and are seen 

 also in the various forms of Sph<srozosma and Leuronema, Their 

 minute size renders any examination of their characters impos- 

 sible. It may be mentioned, however, that they are quite distinct 

 in aspect from the delicate radiating lines frequently met with 

 in the mucous envelope of the majority of the Desmidiaceae. 



Length of joints -0008" to '0009"; breadth of ditto -0012" 

 to -0019". Length of connecting bands -0002" to -OOO-i". 



Lower Bengal, 1855. 



Plate YIII. fig. I. Portion of a filament seen in front view. Fig. 2. End 

 view of a single joint. Fig. 3. Two joints undergoing division. Fig. 4, 

 exhibiting the ap]3earance of a single connecting band. Fig. .5. End view 

 of a joint, showing the pin-like epiphytic growths. Fig. 6. A sporangium 

 just prior to the casting-oflP of the empty parent-joints. 



[All the figures, with the exception of Fig. 4. PL YIII., are magnified 

 400 diameters.] 



[To be continued.] 



XXII. — Remarks on ]\Ir. j\P Andrew's ''Note on the Comparative 

 Size of Marine MoUusca in various Latitudes of the European 

 Seas." By John Gwyn Jeffreys, F.R.S. 



The importance of this question in a geological point of view, 

 and especially with regard to the history of the so-called " Gla- 

 cial epoch," will, I trust, be accepted as my apology for saying 

 a few words on the subject. Although I do not profess to have 

 had the experience of my friend Mr. M'Andrew in dredging in 

 extreme northern and southern latitudes, my acquaintance with 

 the marine Tcstacea of our own coasts, as well as a careful exa- 

 mination of the collections of MoUer, Costa, D'Orbigny, Mr. 

 M'Andrew, and others in the British Museum, with reference 

 to the maximum size of the specimens contained therein, com- 

 pared with those in my own collection of British shells (inde- 



