124 . SIPHO. 



the whorls are more rounded ; the apex is stiliform and prominent ; 

 and the ridges are less crowded, and are sharper and more raised, 

 especially on the upper whorls. The odontophores of the two 

 species also differ. The true Islandicus is a northern species, 

 very rare upon the northern confines of Great Britain. The 

 English species usually known under this name is the S. gracilis, 

 whilst the American species commonly known as S. Islandicus is 

 S. Stimpsoni, Morch. The name of S. cornea, Linn., is excluded 

 because it is believed to have covered more than one species. 



S. GRACILIS, Da Costa. PI. 51, figs. 298, 299, 311. 



White (rarely with a tinge of flesh color) beneath a membranous, 

 yellowish brown or lemon-colored epidermis. Length, 3 inches. 

 Great Britain, 20 to 145 fathoms, rare in the South, 



and on the Coast of France ; Sweden ; Norway ; 



Iceland; MassacJiusetts ; Behring's Straits f 



Jeffreys describes a var. convoluta, which is smaller, narrower, 

 and somewhat cylindrical, more solid, with a longer spire, having 

 sharper ridges and a deeper suture ; mouth proportionally smaller. 

 He thus describes the egg-capsules. 



" The capsules are solitary, small, membranous, pouch-shaped, 

 and attached by a broad base to stones and corallines ; their sur- 

 face is microscopically and closely reticulated ; orifice extremely 

 large and sometimes having the edge partly stained with pink. 

 Each capsule contains only a single embryonic shell, which is 

 transparent, and through it may be seen the orange liver and two 

 unequal-sized plumes of pale yellow gills." 



" Monstrosities now and then occur, viz., some of the ridges 

 being prominent and keel-like ; spire twisted on one side or down- 

 wards ; penultimate whorl swollen ; apex broken off and replaced 

 by a shelly plug ; or the operculum aborted and concave. This 

 whelk is occasionally brought to Billingsgate (London) market, 

 mixed with the common eatable kinds ; but it is not saleable. 

 The fishermen call it l borer.' " 



Kobelt considers the Fusus Islandicus of the American coast 

 the equivalent of this species, and calls it var. ventricoswr ; but 

 two species appear to be confounded in our u Islandicus :" a 

 form which can be readily referred to S. gracilis, and a much 

 larger, more ventricose form which has been separated as a dis- 

 tinct species under the name of Stimpsoni, Morch. 



