On the Structure and Development of Argiope. 495 



is slightly produced. The two oiiter thirds lie against the anterior border 

 of the triangulär areas of the ventral shell. The body of Argiope lies al- 

 most entirely in the dorsal shell whose internai skeleton consists of three 

 triangulär plates: one median, the other two lateral and paired (fig. 16) . 

 The lateral parts of the skeleton consist of two triangulär plates, which 

 have two faces and three borders. The plates pass from the junction of 

 the outer third with the centrai third of the posterior border of the dorsal 

 shell, parallel with the margin of the shell to about the middle of the lateral 

 border figs. 16 and 18 sk). Thus of the two faces, one looks inward, 

 the other outwards. Of the borders one looks towards the median line, 

 another looks towards the ventral shell and the third forms the attach- 

 ment of the piate to the imperforate valve. It is at the angle formed by 

 the first and third of these borders that the notch occurs, into which the 

 teeth of the perforate valve fit. Although these plates do not form a con- 

 tinuous support in front, there are traces of them in the anterior border, 

 in the form of small teeth (figs. 16 and 18). The third part of the inter- 

 nai skeleton also consists of a triangulär piate, its two faces look late- 

 rally, its posterior border is deeply curved and serves to support the 

 anterior part of the alimentary canal. The mouth is situated just behind 

 the apex of this triangle , where the posterior border joins the upper. 

 This latter border slopes gradually away towards the anterior margin of 

 the shell, and is cut into a series of sharp teeth in Argiope neapolitana, 

 although in A. cuneata it is quite smooth. This median septum divides 

 the lophophore into two lobes (fig. 1 1 sm) . 



The shell of A. cuneata is about 1 .5 times as broad as long ; there is 

 no median depression on the anterior border Fig. 10) . The posterior bor- 

 der is nearly straight , sloping very gradually towards the aperture for 

 the stalk, there is no pointed b e a k. The shell is radially ribbed, and the 

 ribs are of a bright yellow color while the depressions between them are 

 a light brick red , the same color as the eggs and larvae. The ribs are 

 usually six or eight and lie symmetrical on each side of a median groove, 

 the ribs of both shells correspond, the margins of the shells are not entire 

 as in A. neapolitana but slightly crenate, the projections corresponding 

 with the ribs. 



The internai skeleton consists like that of A. neapolitana of a median 

 ridge on the posterior two thirds of the ventral shell and of three plates 

 on the dorsal shell. The anterior border of the median one forms a 

 much greater angle with the piane of the shell than is the case with that 

 of A. neapolitana, it is also without teeth. In old specimens this piate 

 is supported by two lateral wings. The lateral plates which support 



