ARGIOPE. 



genus in his second order, or Cryptobranchia, stating the oral arms to be "entirely 

 attached in the form of two or more lobed processes sunk into grooves in the disk 

 of the ventral valve." Again Professor King 1 demurs to the order Cryptobranchia, 

 and sides with Professor Forbes, believing Argiope to be a true " brachiferous Pal- 

 liobranch." 2 



The absence of any notice of the loop of Argiope, in the descriptions above referred to, 

 is probably owing to the imperfection of the specimens examined ; from its extreme 

 delicacy it is often broken away, both from recent and fossil specimens. The character 

 of the loop and septa approximates this genus to Thecidea. Much variation appears to 

 exist in the raised septa or ribs in the interior of the smaller valve, which in the recent 

 A. decollata are of almost equal height, 3 but in all the fossil forms, attributed to the chalk 

 by M. D'Orbigny, and in the tertiary A. cistellula, the central rib alone is prominent, 

 while the others are faintly marked, and even imperceptible in most specimens. 

 Dr. Philippi placed the type of this genus, and some supposed similar recent forms, in the 

 genus Orthis, but, as remarked by Professor Porbes, they possess none of the characters 

 of that genus. 



1 King, C A Monograph of Permian Fossils,' Pal. Soc, p. 81, 1850. 



2 Since writing the above, my attention has been called by Mr. Woodward to the circumstance, that 



some of the minutest specimens of A. decollata, brought 

 by Professor Forbes from the Egean Sea, contains the 

 dried remains of the animal : we have examined two 

 specimens in this condition, one of which is represented 

 in the accompanying woodcut. The mantle adheres 

 closely to the shell as in Terebratula proper, and is not 

 seen, except as part of the shell ; its margin is simple 

 and not ciliated: the oral arms and their connecting 

 membrane are very distinct, owing to the colour, which, 

 is darker and redder than that of the shell. The dried 

 cilia (or cirri) present the same glistening appearance as in Thecidea. The arms originate as in Terebratula, 

 on the anterior side of the mouth, and diverge right and left, parallel with the margin of the shell, but at 

 some little distance from it; when they arrive at the raised septa they turn inwards, forming two lobes on 

 each side of the middle line : the outline of the arms is therefore four lobed, whilst in other recent species, 

 A. cistellula, and in the Cretaceous A. decemcostata, which has only one septum, there is probably only 

 one lobe to each arm. The cilia are few and thick. The arms are relatively connected, as in Terebratula, 

 by a membrane filling up the whole interior space, thus forming an apparatus which forcibly reminds us of 

 the Freshwater Polype Plumatella, figured by Mr. Hancock. 



The distinguished Malacologist, M. D'Orbigny, appears to have mistaken the brachial disk of 

 Argiope and the analogous structure in Thecidea for the mantle, and has founded upon these genera his 

 order Cirrhidce, into which he has admitted, in his most recent publications, the genera Hippurites and 

 Sphaerulites, and those species of Diceras tvhich have one valve smaller than the other. 



From the peculiarity of structure above described, we regard Argiope as generically distinct from 

 Terebratula, but belonging essentially to the same family. 



3 For the sake of reference, we have given figures of the interior of the smaller valve of the recent 

 Argiope decollata in Part II, pi. hi, figs. 15, 16, but in which the loop is not introduced. 



