408 MAZATIAN TTJriVALVES 



mig rather tliin, conspicuous, adlierent, of a horny olivaceous 

 colour. Long. "52, long. spir. "32, lat. '63, div. 90°. 



Sab. — Mazatlan ; 5 sp. very perfect ; L'pool Col. (For other 

 localities , V. supra.) 



Tablet 1949 contains the most characteristic specimen. 



485. ToBixiA pGBAjrosA, Val. 



Solarium granosum, Val. Bee. Ohs. vol. ii. p. 269. Described 



as the living analogue of the Italian fossil, S. milligranum. 

 Comp. Solarium fenestratum, Hinds. 



Tablet 1950 contains a fragment of the base of a very distinct 

 species. It is flat, with numerous strongly granular spiral 

 rows, and deeply cut broad interstices. 



Hah. — Acapuleo, Humboldt 3f Bonpland. — ? Mazatlan ; ex- 

 tremely rare, oflf Spondylus ; L'pool Col. 



Family PTEA^IIDELLID^. 



This family, the smaller forms of which are so abundant in 

 our own seas that Clark speaks of it as a "truly British group, 

 which far outnumbers the discoveries of any other country," 

 is probably well represented in most places, but has escaped 

 attention in consequence of the minuteness of most of its 

 members. While the assiduous and almost exhaustive labours 

 of British malacologists have eliminated 44 species, of which 

 Clark regards 20 as spurious, the mere refuse from a few 

 Mazatlan shells has displayed forms which have required the 

 enumeration of 72 species to contain them. All the sectional 

 fonns described from our own seas are here represented, with 

 the addition of some not hitherto distinguished. While rich 

 in species however, the materials at our command were ver\' 

 sparing in specimens, only one (Chrysallida communis, C. B. 

 Ad.), which appears to be littoral in its habits, being at all 

 common. Next to this ranks Chr. ovulum. then Eulima Pdis- 

 torta. What must be the richness of the ocean bed itself, if so 

 many have left traces of their existence on the backs of a few 

 oysters ! 



The generic distinctions in this family, as in Helicidse and 

 Veneridffi, are confessedly of little value. Links are found 

 which unite all that have been yet proposed. When however 



