240 Mr. W. King on some Shells and other Invertebrate Forms 



terior half of the shell, which I suspect is the same in C. faba, as 

 its anterior muscular impressions are, in proportion, equally as 

 elongated as those of C. marmorata. Notwithstanding there being 

 so little difference between the animal of Crenella marmorata and 

 that of Modiola vulgaris, I am somewhat in favour of generically 

 separating the two groups represented by these species, as they 

 may be readily distinguished from each other by the shells of the 

 one being for the most part externally striated and having ge- 

 nerally crenulated hinge-plates, and those of the other being ex- 

 ternally smooth and possessing plain hinge-margins. If the 

 generic value of the former group be admitted, the law of priority 

 requires us to adopt Capt. Brown's name Crenella for it, while 

 I that of Modiola must be restricted to the latter. 



Leda minuta = genus Lembulus, Leach = Nucula, auct. 



This species is rather rare on our coasts, and is generally brought 

 up from a depth of from twenty to forty fathoms : my largest spe- 

 cimen measures |- and y 1 ^ by § ths of an inch. 



With the exception of Dr. Leach and Mr. J. E. Gray*, none 

 of our British conchologists have thought it necessary to sepa- 

 rate generically the rostrated Nuculas from the rounded ones, 

 which is remarkable, considering the two kinds differ from each 

 other in more respects than that of external form. The rounded 

 Nuculas have an iridescent inside and an entire pallial line, 

 whereas the rostrated ones are of a milky hue internally, and 

 the pallial line has a more or less deep sinus : this difference in 

 the pallial line indicates that the animal of the latter is fur- 

 nished with siphons, as first pointed out by P. C. Mollerf, and 

 that the animal of the former is without them J. Considering 

 these differences, it cannot but be admitted that the genus Leda, 

 which Schumacher long ago proposed for the rostrated Nuculas, 

 ought to be adopted: Lembulus is Dr. Leach's name for the 

 same group, but as it appears never to have been published, 

 except by other parties and at a date subsequent to the publica- 

 tion of Schumacher's, it necessarily falls to the ground. 



Besides Nucula and Leda y another genus has been proposed by 



* Since writing the above, I have read with pleasure Professor E. Forbes' 

 remarks on this genus. Nearly two years ago, I had a paper prepared on 

 a new genus for the Nuculas with a pallial sinus, which would have been 

 sent to the ' Annals ' but for accidentally finding among some packing-paper 

 of a German book parcel a copy of the first number of Dr. Menke's 'Zeit- 

 schrift fur Malakozoologie,' which made me acquainted with the fact that I 

 had been anticipated both by Schumacher's Leda and Moller's Yoldia. 



f Index Molluscorum Grcenlandia. 



% Mr. R. Garner groups Nucula with the shells which have " a mantle 

 without separate orifices or tubes" (vide Transactions of the Zoological 

 Society, vol. ii. p. 101) ; but Nucula margaritacea has a pedal, an ingress, 

 and an egress orifice. 



