ARGIOPE. 17 



Risso called the present species T. emarginata ; Mr. 

 Lowe described the young as T. cost at a ; Schlotheim 

 appears to have given the name of T. chrysalis to the 

 young of the variety septentrio?ialis ; and Dr. Leach, 

 with his unfortunate propensity to substitute new for 

 old and well-known names, rechristened the species 

 T. striata, adding that it inhabits the " western coasts 

 of Devonshire " ! 



Genus II. ARGI'OPE * Deslongchamps. PL I. f. 2. 



Body compressed : mantle closely adherent to the shell 

 throughout : arms short ; tentacles so minute as to be almost 

 imperceptible. 



Shell obtusely triangular : beak more or less produced : 

 foramen large : hinge-line wide and often straight : skeleton 

 composed of transverse ribs, which are united to longitudinal 

 ridges or septa. 



The members of this genus are much inferior in size 

 to those of Terebratula. Some are ribbed, and others 

 smooth. Deslongchamps founded the genus in 1842; 

 but D'Orbigny, apparently being unaware of that cir- 

 cumstance, proposed, five years afterwards, another name 

 (Megathyris), deriving the characters from the same 

 type. The chief difference between this genus and Te- 

 rebratula consists in the latter having the mantle free 

 at the outer edges, while in the former it adheres 

 throughout to the shell, as well as in the large and wide 

 rostral opening in Argiope, and its marginal and inter- 

 rupted skeleton. 



* From the appearance of white holes in the outer surface of the shell. 



