NUCULA 



Pectunculus in his Area ; we shall, however, in describ- 

 ing Nucula, point out the distinguishing marks, but we 

 must first make some general observations on the Genus 

 as it stands in Lamarck, where it appears to us to consist 

 of shells of three distinct characters: first, of shells 

 whose general form is lanceolate ; these are nearly equi- 

 lateral, much broader than they are long, nearly hyaline, 

 very thin, have no epidermis, and are marine ; secondly, 

 of shells which are decidedly inequilateral, whose pos- 

 terior side is rounded, and whose anterior side is pro- 

 duced into a strongly marked beak, and rather pointed; 

 these, moreover, are covered with a strong epidermis, 

 and though we do not venture to pronounce them fresh 

 water shells, we must assert that there are strong reasons 

 for believing some of them at least to be so, a conclusion 

 to be gathered not only from the peculiarities of the 

 shells themselves, but also from their history which has 

 been handed down to us by Schroter, who called one of 

 them Area fluviatilis, and says of it, that it is found in 

 the rivers of the Coromandel coast; this has been called 

 Lembulus, by Leach : thirdly, the small, obtusely ovate, 

 inequilateral shells, of a pearly substance within, covered 

 with a strong epidermis, unquestionably marine, and of 

 which, one was formerly Lamarck's type of the Genus, 

 and ought, indeed, even now to be considered as such, 

 because it has suggested the generic name; it is the Area 

 Nucleus, Linn., and Nucula margaritacea, Lam. 



Notwithstanding the peculiarities of the three kinds 

 of shells above mentioned, we do not feel authorised to 

 separate them into so many genera, but still we think 

 they may be considered as divisions of the Genus. 



All the shells that have hitherto been associated in 

 Nucula are equivalve, inequilateral, transverse, and 

 generally thin : by far the greater number are covered 

 with a strong olivaceous epidermis. Hinge linear, nar- 

 row, divided into two parts, one posterior, and the other 

 anterior, by an obliquely produced central pit, to which 

 the internal ligament is attached; lateral teeth on each 

 side numerous, acute, rather recurved, locjiing together 

 alternately. Umbones, or beaks contiguous, not sepa- 

 rated by an area as in Area and Pectunculus. Muscular 

 impressions two, simple. Impression of the muscle of 

 attj[K;hment of the mantle without any sinus. The animal 



