MAZATLAN UNIVALVES 397 



may adopt both forms of marginal insertion at different periods 

 of growth, which is contrary to our observation in the young 

 of other species ; or (2) that a different creature, belonging by 

 its plates to one genus, puts on the exact appearance of a species 

 in another, even to the very conspicuous scales, which are for- 

 bidden by the diagnosis to Lepidopleurus, and are also striated 

 which is equally forbidden in Lophyrus. Under either suppo- 

 sition, it would appear that we have not yet attained a correct 

 knowledge of the principles of division to be adopted in this 

 most remarkable familj'. Long. '13, lat. '08, alt. .025. 



Sab. — Mazatlan ; on Spondylus calcifer, extremely rare ; 



L'pool Col. 



Tablet 904 contains the perfect specimen, kindly presented 

 by T. Nuttall, Esq. Of its habitat nothing is certainly known. 

 The Avicula to which it adhered was exactly like the Mazat- 

 lan shells ; and there were also found on its surface several 

 specimens of Septifer Cumingianus, and two of a species of 

 Caecum, both identical with those from Mazatlan. 



256. .? Lepidopletteus Beanii, n. s. 



? L. t. ovatd, elevatd fad angulam Wff^) , fusco-olivaced, seu 

 alhido cceruleoque maculafa ; valvis intermediis valde mxicrona- 

 tis, interstitiis curvatis, inarginihus suhrotundatis ; valvd pos- 

 ticd depressd, excavatd, mucrone miiiimo, siqjeriore ; jugo et 

 areis laterallhus indistinctis : superjicie totd granulis instructd, 

 et punciulis minimis confertim ornatd : valvaruni lobis magnis, 

 curvatis, sinu planato ; marginibus acutis, Jisstiris circiter x. 

 valvis terininaHhus, tmd in titroque latere, intermediis ; margini- 

 bus externis prominentibus ; limbo pallii piluloso, spimdis par- 

 vis, erectis, planatis. 



Differs from L. Mac-Andrei in being longer, with the valves 

 mucronated and rounded at the extremities, the posterior 

 being hoUowed out, and the rest much elevated, without con- 

 spicuous middle portion or lateral areas. The only perfect 

 specimen found (on Acmrea fascicularis) displays no trace of 

 solid scales. The account of the interior is taken from a large 

 central and small anterior valve supposed to belong to this 

 species from their agreement in other respects. Long. '23, 

 lat. • 13, alt. -04, 

 Sab. — Mazatlan ; extrcmclj^ rare ; L'pool Col. 



Tablet 905 contains the perfect specimen off Acmaja, and 

 the two valves. 



