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Description .- "P. testa orlDiculari, tunida, decuEsatim striata, 

 alba; maonlis spadioeis lon-^itudinalibus fasciculatis; natibus lira- 

 menti extrematate antica iiifleris." (Lamarck, 1819). 



The Bovi'den specimens are of rnediiun size, sifocircular , the 

 height virtually equaling the length, decidedly convex; mnbones low, 

 mixch inflated, opisthogyrate, placed slightly behind the median 

 horizontal, almost in contact; anterior rlorsal marp-in longer than 

 the posterior, -//ith a more gf-ntle slope to the lateral marrin; 

 slightly produced posteriori;;, biit rounded; evenly roimde'^. anter- 

 iorly and ventrallj; external surface sculptured v;ith twenty-four 

 to thirty almost equally spaced -orir.ary radiating ribs, on young 

 shells sharply defined and narrow throu.ghout, on adults most con- 

 spicuous on the umbonal slopes, be comiiig very lov7 and relatively 

 broad distally, broader than the interspaces, with a median or sub- 

 melian groove on the clistal tv/o- thirds ; Secondary radials, extend- 

 ing about four-fifths of the distance from the margin to the ujnbo, 

 occasionally present; concentric sculpture of fine striae impress- 

 ed on the radials, ;rodu.eing a cancellated effect; cardinal area 

 narrow, deenly impressed, confined to the area immediately uiider 

 and before the imbo ; hinge plate gently arched; teeth in tv;o series, 

 the anterior conve-, including fifteen teeth, the five nearest the 

 umbo vertical and small, the remainder coarser and tyx)ically glycy- 

 meroid; posterior series shorter and less convex, \7ith nine rela- 



