SPECIES OF PISiniUM. 17 



M tiller's original description (123, ii, p. 205) is as follows : 



" Tellina testa subcordiformi, transversim sulcata s umboue 

 obtuso .... diam. 1-5 lin. 



Testa minus globosa, umbonesque minus gibbi, quarn in 

 T. rivcili \_=Spluer. corneuni], quam maxime refert ; alba, 

 fusca & lutea variat; costa nigricans sirailiter in hac, in 

 quibusdam duplex, simplex vel nulla ; lineis transversim 

 elevatis quasi imbricata, intus glabra, subcrerulea. 



Cardinis denticuli sex vel octo cum fossulis excipientibus, 

 in altera nempe valvula utrinque dens solitarius, ac medio 

 cardine denticuli duo, approximate; in altera utrinque denti- 

 culi duo. Testae juniorum Candida?, pellucidoc." 



To this it may be well to add Jenyns' fuller description (83, 

 p. 310) of the exterior of the shell, that stands in need of no 

 further amplification so far as regards British forms : 



" Testa paulo variabilis, ovalis, vel oblique trigona, distincte 

 inaequilateralis, ventricosa, antice planiuscula, pulchre stria ta 

 hie -et illic sulcis profnndioribus ; cinerascenti-fusca, maculis 

 et zona marginali lata pallidioribus, interduni nitide lutes- 

 centibus ; rarius omnino fuscesceus aut lutescens ; intus 

 ca3rulescens : umbones obtusi, sorde ferruginea .... stepo 

 incrustati." 



On the other hand, a more detailed diagnosis of the hinge is 

 necessary : 



Hinge (PL I, f. 1 ; III, f. 1) a little more than f the length 

 of the shell, wide, solid, and projecting well inwards ; moderately 

 curved. 



11. Y. a. i. a little more than 1 the length of the hinge-line, stout, 

 curving inwards ; base strong and swollen ; apex on 

 distal side of centre, prominent, bluntly obtuse ; ridges 

 rounded, distal sloping at first steeply, then very 

 gradually, umbonal descending fairly steeply to a lower 

 level than the distal. 



a. in. about | the length of a./., from which it is separated 

 by a deep fossa, somewhat apposed to the shell-margin ; 

 base becoming confluent with that of a. I. towards the 

 umbo ; ape.v on distal side of centre, moderately 

 prominent ; ridges fairly sharp-edged and steep. 

 3. prominent, sharply flexed and deeply notched under 

 the umbo. a lamelliform, sharp, higher towards the 

 middle, running diagonally forward from the umbo, at 

 a high angle, half across the hinge-plate, b spreading 

 out in triangular form from the umbo to the inner 

 margin of the hinge-plate, its sides rising in ridges 



c 



