298 INVERTEBRATA OF MASSACHUSETTS. 



enlarged into strong, wing-like varices ; these are crossed by equi- 

 distant, revolving threads, which together form a network over 

 the shell ; aperture inversely ovate, rounded behind, and pointed 

 before ; outer lip thick, margined within by raised granules which 

 alternate with the external lines ; pillar lip curved, flattened and 

 smooth, and, with the throat, is bluish-white ; canal about the 

 length of the spine, straight or a little recurved, narrow, deep, and 

 partly closed over by the continued lips. Length 1 inch, breadth 

 inch, divergence 60. 



Found sparingly on the shores of Buzzard's Bay, Nantucket, 

 and Martha's Vineyard. According to Mr. Say, it is abundant on 

 the Southern coast. It is the only species known on the coast of 

 the United States, and, as a species, is peculiar on account of the 

 prolongation of its canal. 



Mr. Sowerby regards it as identical with R. muriciformis, Brod., 

 from Western Columbia. The alliance is very close, but ours is a 

 much more delicate shell. At any rate, Mr. Say's description was 

 published ten years before that of Mr. Broderip. 



FAMILY ALATA, LAM. 



Shett with a straight canal at the front of the aperture ; outer lip changing 

 its form and becoming broadly expanded by age. 



GENUS ROSTELLARIA, LAM. 



Shell turreted, spire long, aperture long and narrow, terminat- 

 ing in a straight canal in front, and in a channel running up the 

 spire posteriorly ; outer lip thickened and widely dilated. 



ROSTELLARIA OCCIDENTA'LIS. 



Shett spindle-shaped, the outer lip expanded into a broad, thick 

 wing ; whorls convex, with numerous waving, longitudinal folds, 

 and regular, conspicuous, revolving lines. 



FIGURE 205. 

 State Coll., No. 2. Soc. Cab., No. 3364. 



Rostellaria (Aporrhais) occidentalis, BECK ; LyelVs Catal. of Fossils of St. Law- 

 rence Bay, in Geolog. Trans. GUERIN ; Mag. de Zool., May, 1836, pi. 72. 



