MUSEUM OF COMPARATIVE ZOOLOGY. 281 



Cetoconcha the ventral body wall externally gathered along a line into pinched- 

 up laminae which develop at opposite ends of a lateral line, with a supplemen- 

 tary second line corresponding to the branchial appendix ; finally, the posterior 

 consolidation of the series into a small gill free from the ventral surface except 

 at its proximal extremity, as in Lyonsiella and Verticordia. 



The incurrent siphon is long, retractile into the cavity between the sides of 

 the mantle, the excurrent siphon much shorter ; around their bases is a series 

 of stout (in C. elongata arborescent ?) darkly pigmented tentacular appendages, 

 with smaller papillae inside from them, but no visible ocelli ; the mantle from 

 below the mouth backward is open for two thirds the distance to the siphons, 

 a marked distinction from Verticordia and its congeners ; its margin is plain 

 and not very stout ; the intestine passes through the heart, below which are 

 two glandular brown feather-shaped renal organs ; the liver, ovaries, and 

 muscles are well developed, but a large part of the body cavity is vacant, and 

 its walls are sustained by mesenteric bands or fibrilla; attached to the adduc- 

 tors or the dome of the shell. Type Lyonsia bulla Dall. 



The remarkable characters of this group will be sufficiently evident to those 

 who have a fair knowledge of the macroscopic anatomy of the Pelecypods. 

 Especially do the gills attract attention, and enforce the lesson of the muta- 

 bility of these breathing organs, and their unfitness for use in fundamental 

 classification. 



To Poromya as restricted belong P. gramdata Nyst, P. sublceins Verrill, P. 

 neceroides Seguenza, and P. australis and probably P. Icevis Smith. 



To Cetoconcha belong C bulla Dall, C. tornata (Pecchiolia) Jeffreys, C. nitida 

 {Thracia) Verrill, and C elongata, albida, and margarita, new species. 



The shells grouped by Deshayes, in his discussion of the moUuscan fossils 

 of the Paris basin, under the name of Poromya, form a very heterogeneous 

 assembly, which, in the absence of typical material, would be difficult to 

 assort properly. 



Poromya granulata Nyst and "Westendorp. 



Poromya granulata Nyst and West., Dall, Bull. M. C. Z., IX., p. 108, 1881. 



Corbula gramdata Nyst and West., Nouvelles Res. dcs Coq. Foss. d'Anvers, p. 6, 



pi. iii. fig. 3, 1839. 

 P. anatawides Forbes, ^gean Rep., 1844, p. 103. 



Habitat. Sand Key, 15 fms. ; Station 36,84 fms.; Station 9, 111 1ms.; 

 Station 5, 229 fms.; off Sombrero, 72 fms.; temperatures at bottom 49°. 5 to 

 60°. F. 



Variety P. australis Smith.* 



Habitat. Barbados, 100 fms.; off Sombrero, 54 fras.; Station 20, off Bahia 

 Honda, Cuba, in 220 fras., living, bottom temperature 62°. F.; Station 202, 

 off Grenada, in 92 fms., sand, same temperature. 



* Poromya australis Smith, Chall. Lam., p. 64, pi. xi. figs. 2 a,2 b, 1885. 



