51 



in the centre. It is a thicker shell than the last, with the 

 auricles much smaller, and on the whole more ventricose. 

 Some young specimens were brought from the Philippine 

 Islands by Mr. Cuming. 



16. P. ASPERSUs. (pi. xix. f. 198, 199.) Soiv. Zoo\. Proc. 

 1835. p. 110. 



" T. sub-orbiculari, depressiuscula, sub-eequivalvi, eequilate- 

 rali, auriculis ineequalibus, dextra majuscula, valvarum altera 

 radiatim costata, pallescente seu alba, costis quatuordecim 

 majoribus, rotundatis, lasvibus, altera radiatim costata, costis 

 quindecim acutioribus, fuscis, punctulis Cccrulescentibus asper- 

 sis, interstitiis tenuissime transversim striatis, pallescentibus : 

 long. 1. 4.; lat. 0. 5.; alt. 1. 3.; poll.'' 



This must be distinguished from P. aspersus. Lam. that 

 author having applied that name to the species which had been 

 previously named " danicus" by Chemnitz. It is rather ine- 

 quivalve ; the rays in the upper valve are more acute than 

 those in the lower. Tumbez, Peru. 



17. P. Nucleus, (pi. xiv. f. 85.) Born. Mus. Caes. t. 7- 

 f. 2. Ostrea turffida, dubia ? guttata ? conspersa ? Gmel. 



T. rotundata, ventricosa, sub-cEquivalvi, crassa, costis octo- 

 decim ad viginti, elevatis, sub-quadratis, concentrice striatis ; 

 interstitiis mediocribus; auriculis parvis, sub-cequalibus, sul- 

 catis, rectangulatis ; colore griseo nebuloso, fusco-maculato. 

 Variat albo-rufescente, rubro-maculato. Long. 1. 50.; lat. 



0. 90.; alt. 1. 45.; poll. 



Rounded, ventricose, nearly equivalve, thick ; having 

 from 1 8 to 20 ribs, which are elevated, nearly square and con- 

 centrically striated; colour grey, clouded with greyish brown; 

 or nearly white, clouded with reddish brown. 



18. P. ciRCULARis. (pi. xii. f. 23.) Soiu. Zool. Proc. 

 1835. p. 110. 



"T. sub-orbiculari, tumida, sub-eequivalvi, eequilaterali, fusco 

 alboque variegata ; auriculis magnis, sub-sequalibus ; costis 

 radiantibus octodecim ; interstitiis latioribus, arcuatim striatis ; 

 valva altera sulcis profundioribus : long. 1. 5.; lat. 0. 8.; alt. 



1. 4.; poll." 



This species is not so rounded as P. Nucleus, and the auri- 

 cles are larger and less obtuse. " Found in sandy mud at a 

 depth of 7 fathoms." California and St. Vincent's. 



19. P. VENTRicosus. (pi. xii. f. 18, 19, 26.) nob. P. tumi- 

 dus. Sow. Zool. Proc. 1835. p. 109. 



" T. sub-insequivalvi, gequilaterali ; auriculis magnis, sub- 

 sequalibus ; valva altera turgida, fusco-rufescente albidoque 



