OF THE FAMILY OF NAIADES. 447 



made. That of Mr Hyde is a large, old, and valuable speci- 

 men, Lnt has lost some of its important characters. Both 

 Avings are destroyed, the beaks much eroded, and the epider- 

 mis black and much wrinkled, and the rays obsolete. The 

 remarkable waves at the base of the posterior wing are almost 

 obsolete, and the beauty of the nacre nearly destroyed by be- 

 ing thick and opake; cicatrices very perceptible. In this 

 specimen, and I believe it will occur in all adult individuals, 

 the only remains of the lamelliform tooth are in the termina- 

 tion of it under the ligament, about an inch long; the rest 

 of it is lost in the callus of the dorsal margin. Its dimen- 

 sions are 

 Diam. 2-1, Length 5-5, Breadth 7-1 inches. 



In general form and character this species exteriorly resem- 

 bles most the Sym2)hynota alata ; interiorly, except in colour, 

 the Sympliynota l8E.vissima, herein described ; the shape of the 

 lamelliform tooth of which assimilates to it, with the excep- 

 tion of its being double. The teeth in both these species de- 

 scribe nearly the same arc and take the same position. Both 

 species are alated anteriorly and posteriorly to the beaks. 

 The Isdvissima differs in having no undulations, and possessing 

 obsolete rays, double teeth, and purple nacre. 



The Dipsas plicaliis of Leach bears a strong resemblance 

 to this shell. It differs, however, in the wings of the D. pli- 

 catus not being elevated, almost forming a line with the 

 beaks, in the latter not being connate, and in not being crown- 

 ed with undulations at the beaks. His description, however, 

 is so short and defective, and the drawing evidently so badly 

 executed, that I cannot determine in what other points it 

 may differ. 



Schumacher's Cristaria tuherculata bears a strong affinity 

 to this species also, as well in his description as his plate. He 

 describes and figures it, however, as being alated posteriorly, 

 and not anteriorly, and does not mention its being connate. 

 The fact of its possessing a divided lateral tooth, " callus pa' 

 rallelus bifidus," proves that it is not our species. 



VOL, in. — 5 X 



