MAZATLAX BIVALVES 123 



investigated. The ]S'. Zealand specimens appear intermediate 

 between tliis and the typical form, differing from the latter in 

 being a flatter shell, with a well ronnded posterior margin. 

 This shell appears to take all allowable forms except the typi- 

 cal one, the margins never being so straight and angular, and 

 the diagonal keel being less impressed. The muscular impres- 

 sions vary sQmewhat, the posterior adductor beiug generally 

 retort-shaped. The young shells display a fine olive spotting 

 on a light groimd in the x^osterior part, which is always much 

 produced. The largest specimen (distorted) measures long.2'b, 

 lat. 1-2. alt. 1-1. 

 Hah. — Mazatlan ; not common ; L'pool Sf Havre Coll. — ? New 



Zealand, Hincks. 



Tablet 559 contains 1 adolescent specimen, oval form. — 

 560, 2 sp. broad, dorsal margin straight.— 561, 2 do. very 

 long. — 562, 2 sp. slightly curved. — 563, 2 do. ventral margin 

 much incurved. — 561, 1 large specimen, somewhat distorted. 



Tablet 565 contains a valve '05 long, of a oval form, with 

 the concentric furrows clearly marked. 



Gents CEENELLA, Broicn. 



Crenella, Brown, 1827. — Lanistes, Stcains. 1840, (non Monff.) — 

 Lanistina, Grray, 1847. — Myoparo, Lea, 1833.— Modiola, sp. 

 Lam. 



172. Ceenella coabctata, DJcr. 



Dunker in lit. — No. 185, 190, Mus. Cuming. 



Comp. Modiola Chenuauus, .B/c?. = My tilus C, B. M. Cat. 



D'Orh.3foll.-p.8i,7b4,. 

 Comp. ]\r. opifex. Say. 



SheU very variable in shape, but generally very tumid, with 

 a medial constricting line, between which and the anterior 

 part it is nearly smooth : tlie rest with rather fine radiating 

 striae, divaricating on the diagonal angle, which in adult sheUs 

 is clothed with a very coarse bristly epidermis. The ptria> on 

 the dorsal part, which is much hollowed by the protuberance 

 of the umbos and the diagonal angle, are somewhat decussated. 

 It appears to have the power of burrowing, like Lithophagus, 

 'a specimen having been so found in the umbUical portion of 



