52 



variegata, radiatim octodecim costata, costis superne planulatis, 

 interstitiis transversim striatis, altera turgidiore, albicante, 

 radiatim sulcata ; costis interstitialibus latioribus, planulatis, 

 lateralibus fusco-variis ; marginibus ventralibus acute dentatis : 

 long. 1. 75.; lat. 1.; alt. 1. 75.; poll." 



"Found in sandy mud at from 6 to 10 fathoms." The 

 above name is given on account of the name "tumidus" 

 having been previously applied to a small lenticular species. 

 It differs from P. Nucleus in having one valve much more ven- 

 tricose near the apex than the other, in the more trigonal 

 shape, and in the greater flatness of the ribs: it is also gene- 

 rally a much larger shell. St. Elena ; and young specimens 

 brought from Calapan, Philippines, by Mr. Cuming. 



20. P. irradiaxs. (pi. xvii. f. 139, 140.) Lam. Anim. s. 

 Vert. vi. p. 173. P. turgidus, Sow. Genera of Shells. P. 

 concentricus, Say. 



T. rotundata, ventricosa, sub-tenui, concentrice minute 

 striata ; auriculis sub-eequalibus, striatis, anticis minoribus, ad 

 basin emarginatis ; costis octodecim, rotundatis ; interstitiis 

 latis. Long. 3. 80.; lat. 1. 35.; alt. 3. 50.; poll. 



Rounded, ventricose, rather thin, concentrically and 

 minutely striated ; the auricles are nearly equal, the anterior 

 rather the smaller ; and in both valves emarginated at the 

 base ; the ribs, 18 in number, are rounded, with wide interstices. 

 The colour is pale reddish yellow, nearly covered by broad 

 bands and large patches of greyish and reddish brown, a 

 larger portion being left nearly white in the lower valve. 



Mediterranean and Newhaven. 



21. P. ptjrptjratus. (pi. xv. f. 113 and pl.xvi. f. 123 — 125.) 

 Lam. Anim. s. Vert. vi. p. 166. 



T. rotundata, ad latera expansa, ventricosa, crassa ; auriculis 

 sub-eequalibus, radiatim costatis, ad basin emarginatis; costis 

 viginti-duobus, latis, complanatis ; lateribus valde serratis, 

 interstitiis angustis, in medio serratis, ad marginem dentatis ; 

 colore purpureo, albo nigroque maculato ; variat aurantiaco 

 et etiam albo occurrit. Long. 4. 80. ; lat. 1. 70. ; alt. 4. 15. ; 

 poll. 



More spread at the sides than the last, and thicker, with 

 the ribs, 22 in number, broad, flattened on the top, with 

 serrated edges ; the interstices are narrow, having a small 

 serrated rib in their centre. The ground colour is pale purple ; 

 the ribs are ornamented with strongly marked festoons of 

 white, purple and blackish brown. Bay of Callao, Peru. 



22. P. gibbus. (pi. xii. f. 1, 2, 17, and pi. xiv. f. 76.) Linn. 



