MAZATLAN UNIVALVES 483 



seu rarius virescente ; superne conspicue angulato, carind tuber- 

 culosd ; tuber culis plerumque viii. compressis, plus minusve 

 conspicuis, costis radiantibus, scepe subobsoletis, convent entibus ; 

 lirulis spiralibus confertis, supra carinam minus conspicuis, 

 rotundatis, squamosis cinctd, quarum interdum in. infra carinam 

 majores, quasi carinulce, squamis majoribus tuberculis conveni- 

 entibus ; squamulis lirularum confer Us simis, acutioribus, arena- 

 Us, labrum acutum crenulantibus ; labio simplici, haud extante ; 

 canali elongatd, apertd ; costd plus minusve contorla, rimam 

 umbilicalem scepe form ante : operculo pyriformi, arcuato, nigro- 

 rufcscente ; margine tenui, diaphano, intus rubro tincto ; cicatr. 

 muse, lineis incrementi paucis irregulariter concentricis. 



TLe figures of Blainv. and Kien., drawn from a supposed 

 unique specimen, represent the usual state of this pretty little 

 species much better than that of Reeve which (if the same 

 species) is an aberrant form.* The shell varies extremely in 

 shape and strength of sculpture, but presents a general lozenge 

 outline from the keel which is always conspicuous. Whether 

 the secondary keels are developed on the basal part of the whirl, 

 depends on the individual, and is rarely the case in young shells. 

 Almost all the numerous specimens were copiously encrusted 

 with coralline, so that the beautiful markings are rarely seen 

 except near the mouth. The largest of the specimens mea- 

 sures long. 1'28, long. spir. '6, lot. '88, div. 60. 



A young acuminated sp. *78, '32, '47, 50. 

 A depressed sp. '63, '22,,, '45, 70. 



5.~ Mazatlan, Botta.(P. diadema) Payta ; on the reefs : 

 Cuming. Mazatlan ; common ; L'pool Col. 



Tablet 2262 contains 6 sp, basal keels developed, spire ele- 

 vated. 2263, 5 do, less elevated. 2264, 5 do. depressed. 2265, 

 5 do. basal keels scarcely marked. 2266, 5 sp. base plain, much 

 depressed. 2267, 6 do. less depressed. 2268, 4 do. acumi- 

 nated. 2269, 6 sp. shewing the lip in different stages of growth. 

 2270, 3 do. mouth highly coloured. 2271, 1 do. canal twice 

 formed. 2272, 2 sp. much incrusted. 2273, 3 sp. adhesions 

 incommoding the mouth. 2274, 4 sp. mended after fracture. 

 2275, 1 sp. curiously worm-eaten. 2276, 8 normal opercula. 

 2277, 4 do. somewhat irregular ; one with nucleus subcentral. 



* Perhaps the tickets of the types in Mus. Cuming have been displaced. 

 Reeve gives the shell as S, American : but the "Cunm diadema, Lam." of the 

 collection is ticketed "Mauritius," and is certainly distinct from the Mazatlan 

 shell. The latter more nearly resembles C. caleaiy.Z7rod, in the collection. 



