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BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



of which prolongs the other, are very often unequal, the distal hook being more 

 strongly marked; under these hooks the roughness of the surface of the spine often 

 grows into minute teeth, which are very distinct, there being one or two on each 

 side. The third spine and also the following one present about the same shape; 

 however there is a decreasing tendency in the size of the terminal hooks. The two 

 succeeding spines still offer at their ends two or three small denticulations, but these 

 are very fine and do not incurve sideways. The last dorsal spine, smaller than the 

 others, is almost cylindrical, and its rounded end may still show a very fine spinule. 

 The tentacular pores are very short, and the ambulacral tubes are large. As a 

 general rule, there is but one tentacular scale; it is very small, flattened, slightly 

 elongated, and rounded at its end, which is rough; it issues from the lateral plate. 

 On the first pores a second scale is often found, smaller, rounded, issuing from the 

 under plate. This second scale is always lacking on the first brachial pore, and is 

 not even constantly present on the succeeding pores. In the following table I give 

 the number of tentacular scales which I observed on the first articles of each arm 

 on each side: 



Connections and differences. A.fibulata belongs to the section of the Amphiurx 

 s. str., and must be classified under such Amphiurse as have tentacular pores offering 

 but a single scale; but it is distinct from all the species of the same group by the 

 size of the tentacular pores, which contrasts with the reduction of the tentacular 

 scale; by a second scale occasionally existing on the pores included between the 

 second and the sixth pair; by the smallest of the upper and under brachial plates; 

 by the second, third, and fourth brachial spines wliich are often bihamuled or 

 which offer at least at their ends a little transverse hook; and, lastly, by the slight 

 development of the external oral papilla. 



There is no possibility of A.fibulata having any affinity either with A.flexuosa 

 Ljungman, owing to the presence of plates on the under face of the disk and to the 

 shape of the brachial spines; or with A. palmeri Lyman, the spines of which are 

 not bihamuled; moreover, the mouth shields and the external oral papilla of the 

 latter are of a different shape. 



Owing to the presence of two tentacular scales on the first pores, although 

 their pxesence be occasional, one might perhaps look for some affinity of A.fibulata 

 with such species as have the under face of the disk covered with scales and which 

 possess two tentacular scales on a more or less extended part of the length of the 

 arms. Under such conditions, the species to which A. fibulata would be more 

 closely allied is A. bihamula H. L. Clark, owing to the nature of the spines, but it 

 differs from the latter species through the plates of the under face of the disk not 

 being closely joined, but on the contrary remaining wider and looser than on the 

 upper face; it also differs from it through the radial shields being shorter and wider, 



