S06 Mr. A. Adams on the Species of Nesera 



pluma. Fig. 1 exhibits the polypite exserted from the hydro- 

 theca, and the pseudopodia withdrawn : a a, mesial nematophore; 

 b, lateral nematophore ; c, bulbous termination of the proto- 

 plasmic contents of mesial nematophore, with a cluster of large 

 thread-cells immersed in the protoplasm ; d, point at which the 

 protoplasm of the mesial nematophore may be projected in the 

 form of a pseudopodium through the lateral aperture of the nema- 

 tophore into the cavity of the hydrotheca. The figure represents 

 the condition in which the pseudopodial process is entirely with- 

 drawn. 



Figs. 2-4. Polypite retracted and the pseudopodia in various states of 

 emission : d', pseudopodia projected into the cavity of the hydro- 

 theca through the lateral apperture in the mesial nematophore. 

 In fig. 4, the pseudopodium has become irregularly branched : e, 

 pseudopodia projected into the surrounding water from the sum- 

 mit of the lateral nematophore. 



Fig. 5. Portion of a ramulus of Antennularia antennina with hydrotheca 

 and exserted polypite, and nematophores : a, azygous or mesial 

 nematophores ; b, lateral nematophores in pairs ; d, protoplasm 

 in a state of repose, forming a spherical mass in the distal chamber 

 of the nematophore ; d', protoplasm of the azygous nematophores 

 extended as a digitiform pseudopodium ; e, similar extension of 

 the protoplasm of the lateral nematophores. 



XXII. — On the Species of "N es&ra. found in the Seas of Japan. 

 By Arthur Adams, F.L.S. &c. 

 The species of iVe^ra, properly so called, are less numerous than 

 is commonly imagined. Many shells formerly regarded as be- 

 longing to this genus -have already been distributed among other 

 tribes. For example, N. viridescens, Hinds, N. opalina, Hds., 

 and N. lata, Hds., have been properly referred to Theora, a genus 

 which I consider should be placed in Tellinidse, in close proxi- 

 mity to Abra or Syndosmya. Then, again, N. lyrata, Hds., 

 N. tenuis, Hds, and N.pulchella, Ad. & Rve., have been removed 

 to Raeta, a genus of Mactridse; and now I shall endeavour to 

 show, by an examination of the hinge-teeth and by other cha- 

 racters, that N. cochlearis, Hds., and N. adunca, Gould, consti- 

 tute two small groups in the immediate vicinity of Scrobicularia. 

 The genus even then, when properly restricted, will exhibit 

 forms so dissimilar, or dentition so peculiar, as to require to be 

 thrown into three distinct groups. 



Genus Ne^era, Gray. 



Shell inequivalve. Surface of valves lamellar. Hinge with a 

 prominent cup-like cartilage-pit. Right valve with a posterior 

 lateral tooth. 



1. Nem-a elegans, Hinds. 



N. elegans, Hds. Proc. Zool. Soc. 1843, p. 1^. 

 N. Moluccana, Ad. & Rve. Moll. Voy. Sam. pi. 23. f. 4. 

 //ad. Mino-Sima; 63 fathoms. 



