200 MAZATLAN UNIVALVES 



Shell extremely large ; white, or of a yellowish or greenish 

 tinge, occasionally orange ; with a broad marginal band of a 

 semidiaphanous hue, very conspicuous in the young shell. 

 Muscular scar in adult raised, irregularly lobed and corrugated. 

 The outside is frequently covered with Algae and bored by 

 Lithophagi. Its surface is a favourite place of adherence for 

 smaller limpets. In the young shell may be traced about 10 

 very indistinct principal ribs, with a profusion of radiating 

 lirulse. These however very soon disappear. The youngest 

 ascertained specimen measures long. 1*65, lot. 1*4, alt. '42. 



The>rgestsp. 9'2, 6*9, 4'5. 



A flatter do. 9', 7'1, 3*6. 



Hob. Mazatlan, Beecheys Voyage. Do., Menke. Do. ; 



abundant, L'pool fy Havre Coll. Monterey, Col. Jewett, 



(G-ould ms. :' non Nutt.) Payta, Peru, jyOrbigny. 



Tablet 908 contains 3 young sp. different ages. 909, 1 sp. 

 finely grown, adolescent, margin flattened. 910, 1 do. margin 

 sharp, muscular scar thick, brownish red. 911, the largest sp., 

 outside riddled by Lithophagi. 



260. PATELLA PEDICULUS, Phil. 



Zeit.f. Mai. 1846, p. 21, no. 8. 



=P. corrugata, Eve. Conch. Ic. sp. 132, pi. 40, f. 132, a, b. (1855.) 

 Comp. P. Araucana, B. M. Cat. D'Orb. Moll. p. 53, [no. 448 : 

 (=however P. zebrina, var., teste Gray in loco.) 

 Shell normally flat, oblong, solid, with 10 stout rounded ribs 

 projecting at the margins, of which 2 are in the axis of length 

 with 4 on each side : ribs and interstices radiately striated : 

 yellowish white, generally with more or less of black or brown 

 tortoise-shell markings within, sometimes with the black be- 

 tween the ribs as described by Phil, and Eve. Sometimes the 

 shell is more rounded and the ribs rather angular, in which 

 state it might be taken for the young of P. Mexicana. Occa- 

 sionally a few other intercalary ribs appear. In a very few 

 unusually large specimens, the ribs are nearly 'obsolete at the 

 margin and the shell is much lengthened. The body mark 

 varies as usual ; when plain, it is gathered into points as in P. 

 discors. The very young shells appear not to develop the ribs 

 marginally, in which state they might be taken for the young 

 of P. discors. The stout ribs of the adult shell however bear 

 no analogy with the very finely marked surface of the latter 

 with its curiously puckered circurn-unibonal portion. With the 



