100 PBOr. p. M. DUNCAN ON THE ANATOMY OF THE 



parallel laminse, separated by corresponding spaces. Tlie laminae 

 of one edge fit into the spaces of the other and opposed plate, and 

 there is much uniting conuective tissue there, in the living form. 

 Above the ambitus, where the coronal plates are broad and 

 low, the following points may be observed at the median suture. 

 On the outside of the test, the aboral-sutural line is longer than 

 the adoral. Seen from within the test, the adoral sutural edge 

 presents a convex surface, and the aboral a slight concavity ; 

 moreover, the edge of the adoral suture slopes from within out- 

 wards, and the aboral face slopes in the opposite direction. 



The adoral edge has on it the projecting lamella, which is con- 

 tinuous with the inner layer of the test, and also three distinct 

 parallel laminae, which are stout, long, and separated by cor- 

 responding spaces. Externally to these is the outer lamella of 

 the test. 



On the aboral edge there are two parallel laminae with inter- 

 vening spaces, and these laminae are distinct from the thin outer 

 and inner lamellae of the test. 



In some plates the number of laminae may be great, but the 

 example given is a very common one. Sometimes the edges of 

 the laminae are crenulate, and the amount of inward and outward 

 slope of the face of the sutures varies. 



The nature of the vertical suture changes towards the apex, 

 where the plates are high in comparison with their breadth. 



The adoral edge, which is the longest, has the inner lamella 

 projecting as a stout process as thick as the narrow, curved, and 

 sharp aboral edge. But the adoral edge has a decided groove ex- 

 ternally to the inward overlapping process. It is into this groove 

 that the aboral process of the actinally placed plate fits. 



Hence at the apex the vertical sutures of the interradia are 

 characterized by decided underlap and elongated dove-tailing. 



The Transverse Sutures of the Interradial Plates. — As a rule, 

 the plates are obliquely placed, and wliether they are so or not, 

 the adoral edges are more or less convex actinally, but the aboral 

 edges are the reverse. Near the peristome the faces of the 

 sutures on the opposed plates are nearly flat, or there may be 

 a very slight projection along the middle of the adoral edge. 



The edge looks homogeneous, and it is only near to the lateral 

 sutures of each plate that a fine lamination presents itself, the 

 commencement of the sutural development already noticed. 

 Every now and then perfectly distinct groups of knobs and 



