MAZATLAN UNIVALVES 307 



stoma.— 1491, 1 sp. on fragment of Spondylus, with Bryozoa, 

 &c.— 1492, 1 sp. on Uvanilla unguis.— 1493. 2 separate sp., of 

 which one has deep sculpture. 



355 i. PBlVONIA PCONTOBTA, Var. INDENTATA. 



B. t. "B. contortce" simili, sedminore ; colore haud rosed; 

 sculptura indentata ; costis paticioribus ; interstitiis profundis, 

 caneeUatis. 



This form would hardly be distinguished as a species from 

 the shell alone, so variable is the sculpture of Vermetidae, 

 even on the same specimen ; but as it is not improbable that 

 the second Bivonoid operculum, which is quite distinct, be- 

 longs to it, it is here kept provisionally separate. It is of 

 smaller growth, and yet of much coarser sculpture ; with a 

 different shade of colour, which in this family appears to be of 

 some importance. Long. "5, diam. aperf. '05. 

 Sab. — Mazatlan ; very rare, on Spondyh &c ; L'pool Col. 



Tablet 1494 contains 3 specimens. 



356 PBlVOKIA ALBIDA, «. S. 



B. t. parvd, alhida ; ahfr. ii. primis IcBvibus, turbinoideis, 

 subelevatis, postea amplectatis ; anfr. normalibus subregulariter 

 spiraliter contortis, marg'tnihis subparallelis, ad sese plerumque, 

 ad concham alienam pa7'um, adharentibus ; rugis concentricis 

 plus minusve expressis, spiralibus nullis. 



Both sculpture, colour and size mark this species as distinct, 

 although only 2 extremely young specimens and one with 

 about 5 normal whirls were found. This measures long. "22, 

 lat. '1, diam. apert. '03. 

 Hah. — Mazatlan : extremely rare, off Spondylus ; L'pool Col. 



Tablet 1495 contains a young and the adiilt specimen. 



357. PBivoNiA , sp. ind. (a.) 



Tablet 1496 contains 2 minute Spirorbiform specimens, and a 

 portion of a separate non-spiral tube, only "02 in diameter, 

 which do not appear to be the young of any of the former 

 species. They are of a pale colour, and are nearly smooth. 



