P A N P vE A. 



Plati; I. 



. Genus TANOP^A Menard. 



Testa bivalvi, bhmisculosa, utrinque hians, laevigata, vel 

 concentiicb nigata, epidermide induta, cardine 

 medio ulraque valvd uiiidentato ; ligamcnto con- 

 spicuo, e.rterno ; impressioiie pallii posiice profunde 

 siimato. 



Shell bivalve, bimiisciilar, gaping at both ends, smooth 

 or concentrically wrinkled, covered with an 

 epidermis, hinge with one tooth in the middle in 

 each valve ; ligament conspicuous, external ; palloal 

 impression with a deep sinus. 



Some of the species included in this monograph are 

 separated under the name Glycimeris in the work of 

 Messrs. Adams. The shells of both genera are stated 

 to be similar, excepting that in P.iNOP^.\ the palleal 

 impression is interrupted. The animals, however, 

 differ in the two genera, the siphons being separated 

 near the extremity in Panopcea and united io their 

 extremity in Gl;/cimer!s. It would be impossible to 

 decide absolutely on the validity of this distinction, 

 which is probably one of degree, and therefore of 

 specific value only, without being able to examine 

 specimens of the siphonal integuments of every species. 

 P.\NOP^.\, tiPEt^GLERi, = Norvegica and its near ally P. 

 Middendorjii are quite northern in their range, reach- 

 ing only tlie northernmost parts of Great Britain, while 

 the other species included by Messrs. Adams in the 



genus Ghjcimeris are tropical or southern, their range 

 extending to South Australia. 



Species 1. (Mus. Brit.) 

 P.\Nor^A Aldrovandi. Pan. testa magnd, altcl, svh- 

 rhomhoided, rectiiisculd, crassd, ]iro/undd ; latere 

 antico breviiisculo, acuminato ; pej-ohlique truncato ; 

 margine dorsali recto ; medio planiiisculo, umhoni- 

 biis ovatis ; latere postico lato, ad terminum sub- 

 arcuato, late truncato, margine dorsali concavo. 

 Alduovand's Panop^a. Shell large, elevated, sub- 

 rhomboidal, rather straight, thick, deep ; anterior 

 side rather short, acuminated ; very obliquely 

 truncated ; dorsal margin straight ; middle rather 

 flat, umbones oval ; posterior side broad, a little 

 arched at the end, broadly truncated, dorsal margin 

 concave. 

 La.maeck. Anim. sans Vert. 

 Panopaa glycimevis, Deshayes. 

 Panopaia riigosa, Valenciennes. 

 Hab. Mediterranean. 



The three large species of this genus are thus dis- 

 tinguished, namely, Panopcra Aldrovandi is broad and 

 deep, short and obliquely truncated in front ; Panopaa 

 Fuvjasii is narrower, nearly equilateral, and not at all 

 oblique ; Panopcea aitenuata is narrow, long, and 

 curved posteriorly, broad and reflected anteriorly. 



April, 1S7;J. 



