Mr. J. Alder on the genus Jeffreysia. 193 



6f valves of the Mollusca, would readily create, or materially 

 assist in creating, such excavations ? But I must note, these 

 perforating " sponges " do not seem to be true sponges — merely 

 species of Cliona — a genus, according to the accurate accounts of 

 Dr. Grant, Dr. Johnston, De Blainville, &c., belonging to the 

 class Zoophytes, and which is described by them as a polype fur- 

 nished with about eight short tentacula. 



Postscript. — In addition to the green insects above men- 

 tioned, I observed in July last, numerous other insects, or rather 

 larvae or Caddises, enveloped in cases made of the Spongilla 

 itself, and living parasitically on that substance, but which I do 

 not remember to have seen before in any other mass of the 

 Spongilla. I preserved several of these in spirits, and recently 

 forwarded them for examination to Mr. Westwood. In a letter, 

 dated February 5, 1851, this gentleman has informed me, that 

 " the second kind is truly a Caddis, and will turn to a species of 

 Phryganea or Mystacida. It is quite certain that it has no sort 

 of relationship with the former green insects. It would be very 

 interesting if you could observe the Spongilla now and at a later 

 period, so as to determine i\\t pupa state of these insects, and if 

 possible, to rear them to the perfect state. I have looked care- 

 fully over Pictet's ' Researches on the Phi-yganida ' without being 

 able to find any larvse precisely agreeing with yours — which are 

 not very remarkable, seeing the peculiar nature of their habitat." 



XVIII. — On the genus Jeffreysia. By Joshua Alder, Esq. 

 To Richard Taylor, Esq. 

 Dear Sir, Newcastle, February 13, 1851. 



It is with great reluctance that I again trouble you with any 

 observations of a controversial nature, but in justice to others as 

 well as to myself, I think it necessary to say a few words in de- 

 fence of a genus of mollusks described by me in Forbes and 

 Hanley's ' British MoUusca ' under the name of Jeffreysia. An 

 account of the animal on which it is founded was published in 

 the 'Annals of Natural History' for May 1844, when I pointed 

 out the propriety of raising it to the rank of a genus. The same 

 view was taken by Professor E. Forbes, and at his request I drew 

 up the generic characters inserted in the ' British Mollusca' ; the 

 privilege of naming it being politely conceded to me as the dis- 

 coverer. More recently Mr. Clark, in a late Number of the 

 ' Annals,' has redescribed the same animal, and has placed it in 

 his genus Chemnitsia * (including the Chemnitzia, Odostomia, 



* To avoid circumlocution I shall here use the name Chemnitzia in the 

 sense that Mr. Clark takes it, though I do not agree in the propriet^' of 

 adopting this name for the whole group. 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. vii.. 13 



