NO. 1139. DEKr-WATER MOLLUSC A VERRILL AND BUSH. 817 



Family LYOXSIELLUXK. 



LYONSIELLA SUBQUADRATA (Jeffreys.) 

 (Plate LXXXVII, tig. 3.) 



I't'ccliiolia si<l></t<adrala JEFFREYS, Proc. Zool. Soc. London, p. S>32, pi. i.xx, lig. 3, 

 November, 1881. Not DALL, Bull. Mue. Comp. Zool., XII, p. 272, 1XS6. 



Our specimen seems to agree in every respect, except size, with the 

 original description and figure as given by Jeffreys, ours being consid- 

 erably larger. 



The ninbo is prominent and the beak is curved strongly forward, pro- 

 ducing a deep lunular area which is denned neither by a groove nor 

 a ridge. The surface is everywhere covered with small bnt prominent 

 granules which are numerous, pretty evenly spaced, and arranged 

 somewhat distinctly in radiating rows which, under the microscope, are 

 defined by slight radial ridges uniting those of the same row. The 

 granulations are easily visible with slight enlargement. Under the 

 compound microscope they have the form of elevated, acute cones and 

 blunt tubercles, their height usually greater than their diameter, except 

 on the umbo, where they are low and rounded. Internally the surface 

 is everywhere marked with small, deep pits looking like punctures 

 made by a fine needle, and corresponding to the external grannies. 

 The hinge margin is thickened and entirely edentulous, as described by 

 Jeffreys. Posterior to the beak there is a distinct groove in the thick- 

 ness of the margin for the reception of a ligament. Beneath the beak 

 there is a slight, oblique, marginal notch or slit for the reception of the 

 resilinm, running back within and underneath the dorsal margin, so 

 that it is scarcely visible in a direct front view. 



This shell appears to be identical with the species originally described 

 and figured by Jeffreys under the name of Pecchiolia sulquadrata. 

 Mr. Ball has evidently found an entirely different species in the Jef- 

 frey's collection under this name, which he has referred to the genus 

 Callocanlia and subgenus Vesicomyn^ belonging to an entirely different 

 family from our shell. In order to avoid confusion the shell examined 

 and described by Mr. Dall should receive a distinct specific name; we 

 therefore propose CaUocardia ( Vcsicomya] dalll. Mr. Dall states that 

 "the sparsely set, microscopic tubercles can only be observed with a 

 magnifier; to the eye the surface looks shining and smooth," which 

 shows the surface to be quite different from that of our shell. In his 

 shell there are also two cardinal teeth in each valve. 



One valve (No. 78800), station 2714, N. lat. 38 22', W. long. 70 17' 

 30", in 1,825 fathoms, 1880. 



North of the Hebrides, in 542 fathoms; and off Cape Mondego in 

 Vigo Bay, in 740 to 1,095 fathoms. "Porcupine Expedition, 1.SG9-70."- 

 Jeffreys. 



Proc. N, M. vol. xx 



