288 BULLETIN OF THE 



branchiae, but the palpi art small, or perhaps obsolete ; on this point my speci- 

 men, which had been dried and soaked out, was not conclusive. The internal 

 cartilage bears a large ossicle as in Lyonsiella ; the beaks are subspiral, and the 

 external ligament coils under them away from the hinge-margin, as in Ceto- 

 concha and other Verticordice. The same uncircumscribed lunular depression 

 and puckering of the adjacent hinge-margin is observable in Mytilimeria, which 

 normally should have, from appearances, a tooth-like projection of the twisted 

 margin as in Phctodon, but which is usually masked by the ligament. The 

 sedentary habit of this mollusk, as in other cases of the kind, has resulted in 

 veiling some of its original characters. It is said to " burrow in sponge," but 

 the spongy substance in which it is found is of its own manufacture, and con- 

 sists of sand grains, etc., entangled in a solidified mucus, which is secreted by 

 the animal, and which, like the byssus, is not affected by water. It is proba- 

 ble that in life the foot is susceptible of much extension. 



The surface of the valves in Mytilimeria is not granulated, but is covered by 

 an epidermis not unlike that of Cetoconcha. It may be recalled that sundry 

 species of Verticordia, Poromya, etc., have a habit of attaching sand grains to 

 themselves by a sort of mucous secretion. The pallial line is barely sinuated, 

 and the shell is thin and internally pearly, though the iridescence is veiled as 

 in Cetoconcha by a non-pearly stratum. It is quite certain that some of the 

 species referred to Mytilimeria would be better placed elsewhere. 



Lyonsiella M. Sars (1872; Pecchiolia G. O. Sars after Jeffreys; Lcevicordia 

 Seguenza, 1876). Shell small, thin ; lunule faint or none; ossicle semicylin- 

 drical, forked behind; external ligament almost none; right valve edentulous, 

 lunular edge a little produced and thickened; left valve with an elongate ob- 

 scure thickening of the hinge-margin under the beak. Soft parts described by 

 Sars (Rem. Forma of Animal Life, p. 25, pi. iii. figs. 21-43, 1872). Type L. 

 abyssicola Sars. North Atlantic. 



To this group belong L. insculpta Jeffreys (1875 -|- L. gemma Verrill, 1880), 

 and probably the following species, known to me only by single valves or by 

 description : L. angulafa Jeffreys (as Pecchiolia), L. mytiloides and azinoides 

 Seguenza (1876). The identification of L. gemma with the earlier described 

 insculpta is from authentic specimens; the figure of insculpta in P. Z. S., 1881, 

 is not very characteristic. 



The following species form part of the Blake collection. 



Verticordia acuticostata Philippi. 



Hippagus acuticostatus Phil. Moll. Sicil., 1844. 



Verticordia acuticostata Dall, Bull. M. C. Z., IX. p. 105, 1881. 



Habitat. Station 31, in 84 fms.; living, at Station 5, in 152-229 fms., coral 

 ooze, off Cuba, in the Gulf of Mexico, bottom temperature 49°.5 F. ; Barba- 

 dos, 100 fms. 



