Mr. J. Alder on new species of Rissoa and Odostomia. 323 



Its powers of life appear considerable, for if placed in a saucer 

 of water after having long been dried, it almost immediately ex- 

 pands and recovers its original form, and its cells imbibe moist- 

 ure more perfectly than those of Algae generally do ; and far 

 more perfectly and readily than any species of Codium, Vaucheria 

 or Bryopsis. It is thus admirably adapted to the circumstances 

 of intermittent nourishment under which it is developed, and 

 affords a new instance, to the many thousands recorded, of peculiar 

 care exercised in providing for the welfare of even the humblest 

 member of the organized world. 



Many interesting additions to our marine flora may be ex- 

 pected from Mr. M^Calla^s researches on the west coast of Ire- 

 land. In addition to the present new species, he has already found 

 fine specimens of some very rare Algse, as Gloiosiphonia capillaris, 

 Conferva rectangularis and others. The last-named plant, ori- 

 ginally discovered by Mrs. Griffiths and Mr. Borrer at Torquay, 

 was, so far as I am aware, first found in Ireland by Mr. Reilly of 

 Cork, who gathered a single specimen in Galway Bay some years 

 ago, and at the same time picked up the so-called Gelidium ? ros- 

 tratum {Heringia rostrata, J. Ag.). W. H. H, 



March 15, 1844. 



EXPLANATION OF PLATE VL 

 Fig. 1. Patch of Codium amjjhibium, natural size. 



— 2. A single frond, magnified. 



— 3. Some of the ramuli of the periphery, magnified. 



XXXVIII. — Descriptions of some new British species of Rissoa 

 and Odostomia. By Joshua Alder, Esq. 



[With a Plate.] 



The genera Rissoa and Odostomia belong to a group of small 

 moUusks which appear to hold their head-quarters in European 

 seas, and more especially on the shores of our own islands. The 

 number of published British species much exceeds that of any 

 other country*, yet several still remain un described in collections. 

 I have drawn up descriptions of the following from my own ca- 

 binet, at the suggestion of my friend Mr. Thompson of Belfast, 

 who has lately ascertained that most of them are inhabitants of 

 the Irish coast. 



Rissoa inconspicua. Plate VIII. fig. 6 and 7. 

 Shell ovate-conical, shining, transparent, yellowish white, with 

 a few blotches of pale fulvous brown occasionally forming two or 



* M. Deshayes, in the 2nd edition of Lamarck's * Animaux sans Ver- 

 tebres,' has published thirty-four recent species oi Rissoa (including Odo- 

 stomia), He has not, however, admitted any British species, except such as 

 have been re-described, mostly under different names, by French authors. 

 The number of British species of the two genera is upwards of forty. 



Y2 



