496 Arthur E. Shipley, 



the lophopbore are perforateci bv two large holes. these are also foimd 

 in the other species, but are there qiiite small. The shelis of both species 

 are slightly transparent so that the outline of the lophopbore and the red 

 ovaries and larvae can be iudistinctly seen throiigh them. Both shelis 

 are marked by faint lines which run parallel to the margin. 



In its minute structure the shell of Argiope consists of a number of 

 very fine calcareous spicules supported in an organic network. The 

 spieules are not very regularly arranged but they bave a general antero- 

 posterior direction, and are oblique, their inner end being- nearer to the 

 edge of the shell, their outer to the beak. Their inner extremities are 

 rounded somewhat enlarged and overlap each other like the slates on a 

 roof (fig. 1 4 1 ; they are much larger at the centre than at the margin of the 

 shell. On the outer side of the shell is a layer. in thickness about one 

 eighth of the whole shell, where the proportion of calcareous matter to 

 organic is euormously increased. The spicules are bere nearly square 

 and packed against one another like bricks. I bave unfortunately beeu 

 unable to see King's paper ^ but I believe this layer must agree with the 

 second layer discovered by him, and mentioned in the recent paper of 

 Van Bemmelen-. 



Outside this is the third layer or periostracum. This is a thick struc- 

 tureless cuticle : it completely covers the whole shell , and in the fresh 

 state adheres very closely to it. The cuticle does not stain ifigs. 1 and lo cu) . 



When sections are made through the decalcified shell , the organic 

 basis or network is seen to consist of numerous very fine homogeneous 

 fibrils. The meshes of the network bave the same shape as the spicules 

 they contaiu and so in longitudinal sections they appear elongated 

 and oblique , in transverse or horizontal sections as irregularly square 

 (fig. 15 and 19 . These organic fibrils are in connection on their inner 

 side with the mantle which lines every part of the shell. They stain 

 very readily with Borax Carmine or Haematoxylin. 



In the decalcified sections there is a cousiderable space between 

 the periostracum and the shell. This may be partly due as Van Bem- 

 MELEN suggests to the disappearance of King's second layer , but it is, 

 I believe , chiefly caused by the evolution of gas forcing the cuticle 

 away from the shell. 



The shell is pierced by very numerous canals which run completely 



1 On the Histology of the Test of the Class Palliobrauchiata. Trans, of the 

 Eoy. Irish. Acacl. Voi. XXIV. 1S67. 



■' Untersuchungen über den anatomischen und histologischen Bau der Bra- 

 chiopoda Testicardijiia. Jeuaische Zeitschrift f. Naturwissenschaft. XVI. 1883. 



