420 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



will however easily be distinguislied from the numerous species of this 

 genus by its elevated triangular ribs, broader at their base than the 

 interstices. 



Pecten macrotis. 

 Fig. 15. 



P. testa subinsequivalvi, sequilaterali, radiatim costata ; costis viginti scabris, dorso 

 acutiusculis, lateribus utroque costellatis, interstitiis angustioribus, costella unica 

 mediana ; auriculis magnis, radiatim striatis, scabris. Long. 1*5, lat. 0*6, alt. 1*6 

 poll. 



Found at Adi9a, so"ath of Lisbon, and near Piedade. This species 

 somewhat resembles P. operciilaris ; it may however easily be di- 

 stinguished from that species by the great depth of one valve and the 

 much larger ears. In Mr. Sharpe's collection. 



Pecten giganteus. 



Fig. 16. 



Pect. testa insequivalvi, valva altera concava, altera planulata, valv93 concavse 

 costis radiantibus 16 s. 17, elevatis, superne subplannlatis, ad latera rotundatis, 

 transverse striatis ; auriculis sequalibus. Long. 6*25, alt. 5-75, lat. 2 poll. 



In general form and in proportions this species resembles Pecten 

 maxbnus ; it may however easily be distinguished by the circumstance 

 of its radiating ridges being destitute of the longitudinal strise so con- 

 spicuous in that species. 



OSTREA CRASSICOSTATA. 



Fig. 23. 



0. testa inaequivalvi, insequilaterali, irregulari, valva altera plano-concava, altera 

 convexa, Isevi, costis crassis irregularibus paucis ; margine crasse undulato ; 

 latere altero alato. 



The only species to which this bears the least resemblance is the 

 Ostrea hyotis, Linn., which is also found at Almada ; we think how- 

 ever that they cannot be confounded together. 



Natica perpusilla. 



Fig. 31 a. mag. nat.— 33 5, c. auctse. 



Nat, testa parva, subglobosa, Igevi, nitida, crassiuscula, spira subconica, anfrac- 

 tibus 2>^, ultimo )naximo, postice obducto ; labio interno incrassato, umbilicum 

 partim tegente; umbilico antice carina obtusissima circumdato. Long. 0-25, 

 lat. 0-2 poll. 



This species is between N. Tiber, Val., and N. conica, Lam., in 

 general form ; its spire is more prominent than that of the first, 

 though less so than -that of the latter ; it may be distinguished from 

 both by its wanting the umbilical callosity. I believe it is the smallest 

 species known. 



SCALARIA TENERA. 



Fig. 24. 



Seal, testa oblongo-pyramidali, tenui, anfractibus septem rotundatis, costellis par- 

 vis, paululiim elevatis, rotundatis, postice mucronulatis. Long. 0*8, lat. 0*35 poll. 



A very delicate little shell, somewhat resembhng the Turbo clathra- 



