91 



well-developed auricle, characters which could not be ascribed 

 simply to immaturity. 



Avicula lurida. T. squamosa, vix obliqua, fere ecaudata, 

 solidula, coloribus rosaceis, viridibus et flavidis radiatim fucata : 

 valva dextra postice vix sinuata, convexa ; auricula lata, triangu- 

 laris ; fissura byssica haud profunda : valva sinistra ventricosa, 

 tuberculo magno subcaudali munita, postice integia : margarita 

 argentea; limbo corticali corneo et nigro marmorato. Long. 2^ ; 

 alt. 2^; lat. § poll. Hab. New Zealand. 



In form it resembles A. fucata ; but its smoother surface, 

 difference of coloration both without and within, and its much 

 more elongated auricle, are quite distinctive. The young stages 

 of this shell are exceedingly beautiful, being rose red, with a sort 

 of superficial radiation of cream-color. 



Avicula glabra. T. tenuis, semi-elliptica, vix obliqua, late 

 caudata, glabra, ad peripheriam lamellata, virescens, albo-radiata : 

 valva dextra planiuscula ; auricula latior quam longa : valva 

 sinistra ventricosa, antice integra, acutangula : cardinis dentibus 

 obsoletis : margarita argentea ; limbo corticali livido-corneo. 

 Long. 2f ; alt. 2| ; lat. £ poll. Hab. New Zealand. 



Outline much as in A. fucata, but the caudal region is much 

 more compressed. Its smooth surface and widely different co- 

 loration are easily recognized. The white radiations are opaque, 

 and have a superficial appearance. 



Crenatula pergaminea. T. membranacea, obliquissima, 

 subfalcata, concentrice laminoso-fibrosa, albida, lineis lacteis 

 radiata ; margine dorsali recto, umbonibus tumidis, acutis, ad 

 trientem anteriorem sitis ; latere antico arcuato et cum margine 

 ventrali continuo ; latere postico oblique truncato ; area cardinali 

 angusta ad 5-crenata : intus sub-margaritacea. Long, 1£ ; alt. m 

 lat. § poll. Hab. Feejee Islands. 



None of the species already described agree with this in color 

 texture, or form. Its structure is very delicate and unresisting, 

 almost fibrous at its edge. 



Perna argillacea. T. solidula, mutica, compressa, elongata, 

 antice dilatata, postice subrecta, ex luteo alutacea, hie illic nigri- 

 cans ; apice adunco : fissura byssali angusta, lanceolata : intus 



