18 TEREBRATULID.E. 



A. Shell ribbed. 

 1. Argiope decolla'ta*, Chemnitz. 



Anomia decollate,, Chemn. Conch. Cab. viii. p.96, pi. 78. i.lOba-d. Argiope 

 decollate,, Jeffr. in Ann. Nat. Hist. 3rd ser. ii. p. 124, pi. v. f. 3 a-e. 



Body reddish-brown : mantle forming a thin film : arms 

 nearly circular, divided into lobes, which correspond in number 

 with the septa in the shell ; cirri few and thick : 'peduncle very 

 short. 



Shell of an irregular shape, varying from round to trans- 

 versely oval, sometimes resembling that of a horse's hoof, 

 compressed, much higher near the beak, and sloping abruptly 

 in a wedge-like fashion towards the front and sides, solid, of 

 a dull aspect : sculpture, 15-20 slight ribs which radiate from 

 the beak but scarcely reach the margins ; lines of growth 

 rather strong or conspicuous ; tubercles large and numerous, 

 the interstices having a frosted appearance arising from a 

 minute granular structure : colour light-brown : margins 

 rounded at the front and sides, so as to form a semicircle, and 

 obtusely angled behind : bealc rather prominent and worn by 

 continual friction ; the under side shows distinctly the layers 

 of increase : foramen exceedingly large, transversely and irre- 

 gularly oval, in consequence of its having been made partly 

 out of the umbo of the lower valve : deltidium scarcely trace- 

 able : hinge-plate remarkably thick and broad : teeth short and 

 triangular: sockets broad and deep: skeleton composed of a series 

 of narrow riband-like plates, which are curved and fit into the 

 hollows between the septa, lying at no great distance from the 

 front margin, and almost touching the shell ; within the upper 

 valve also are five septa, placed at equal distances, the middle 

 and longest of which springs from under the beak ; none of 

 them reach the margin, which is wedge-shaped ; in the lower 

 valve are three strong equidistant ridges, which are placed in 

 the central space ; these are notched in front, crested at the 

 top, and obliquely striate at the sides, where may be occa- 

 sionally observed a few small bead-like tubercles. L. 0*3. 

 B. 0-285. 



Habitat : 18 fathoms, in gravelly shell-sand, two miles 

 east of Guernsey ; rare. This is the most northern limit 



* Truncate. 



