Zoological Society. 65 



des Poiss. ii. 99. pi. 1 ; Supp. to Petromyzon ; Shaw, Gen. Zool. v. 

 pt. 2. p. 261, \S^4.—Ammocoetes branchialis, var., Cuv. Reg, An. 

 ii. 118, 1817. 



Hab. Europe, Seine. 



3. Ammoccetes concoi.or. Mud Eel or Blind Eel. 



Ammocoetes concolor^ Kirtland, Boston Journ. iii. 473. pi. 27. 

 f. 1«, h, 1841. 



Hah. N. America, Mahoning and Scioto rivers. 



4. Ammoccetes bicolor. Coloured Mud Lamprey. 



Ammoccetes hicolovy Lesueur, Amer. Phil. Soc. (N. S.) i. 386. — 

 Ammoccetes bicolor, Storer, Fishes of Massachusetts, 198; De Kay, 

 Nat. Hist, of New York, 383, 679. f. 248. pt. 1 ; Zool. 1842.,^,^^ 



Hab. N. America, Connecticut river. 



5. Ammoccetes unicolor. Plain Mud Lamprey. 

 Ammocoetes unicolor, De Kay, Nat. Hist, of New York, 383. pi. 79. 



f. 2.50. pt. 1 ; Zool. 1842. 



Hab. N. America, Lake Champlain. 



Nov. 11, 1851. — W. J. Broderip, Esq., Vice-President, in the Chair. 

 The following paper was read : — , < 



Descriptions of sixteen new species of Rissoina, '^^** 

 By Arthur Adams, Surgeon R.N., F.L.S. etc. - *^^^ 



RissoiNA, D'Orbigny. yH- — . I h^\ ,(><)<» 



About eighteen species of this genus, as restricted by M. d*Or-' 

 bigny, have been already described, inhabiting various countries. 

 Those here named are a portion of the discoveries made by Mr. Cu- 

 ming among the islands of the Philippine Archipelago, and are many 

 of them of considerable size ; and it is in these that the peculiarity 

 of operculum is best seen. 



The process of the semiovate, horny, subspiral operculum, first 

 pointed out by D'Orbigny, is sometimes very long and slender, and 

 very much resembles in appearance the analogous appendage of the 

 operculum of Nerita and Neritina. The genus Jeffrey sia of Alder, 

 or Rissoella of Gray, has a similar appendage, but the position of 

 the eyes, and the peculiar structure of the fore part of the head, 

 place the latter genus in a different family, viz. Pyramidellidce. The 

 Rissoince may also readily be known from the neighbouring genus 

 Rissoa, by the aperture being somewhat channeled anteriorly, whereas 

 in Rissoa it is continuous and entire. The nature of the animal re- 

 sembles Rissoa, according to D'Orbigny, who places the genus 

 among the MelaniadcE. 



1. RissoiNA plicata, a. Adams. R. testd turrito-subulatd, 



subpyramidaU, albd, sordidd, anfractibiis octo, planis, longi- 



tudinaliter valde plicatd, transversim striatd, plicis elevatis, 



postic^ subangulatis, interstitiis transversim striatis ; aperturd 



Ann, i<s Mag. N. Hist. Ser.2. Vol.xiii, 5 



