DESCRIPTION OF SPINES. 137 



face tubercles which thickly cover the plates of the test in occasional 

 well preserved specimens. The spine tubercles of this species were figured 

 by Roemer (36), and are present in great numbers on the specimen from 

 which plate 4, figure 12, was drawn, and by careful examination these 

 tubercles can be seen in portions of the photographic figure (plate 5, figure 

 18). They served as bases of articulation for hundreds of small spines 

 which covered thickly both the ambulacral and interambulacral areas. 



The specimen showing spines from which plate 2, figure 1, was drawn 

 is a single individual of Melonites muUiporus from the Saint Louis group, 

 Subcarboniferous of Saint Louis, Missouri. It is in the collections of 

 the Museum of Comparative Zoology (catalogue number 2988). The 

 specimen is of the usual type from this locality; close inspection, how- 

 ever, reveals scattered over the test, but more especially in the protected 

 furrows and depressions, innumerable minute spines clinging to the 

 plates of both the ambulacral and interambulacral areas. They are 

 most abundantly and best preserved in the longitudinal furrows formed 

 by the depressed, irregular, lateral plates of each ambulacrum. A cluster 

 of these spines is shown in plate 2, figure 1, magnified 6 + diameters. 

 The well preserved spines are cylindrical, somewhat swollen at the base, 

 and gradually taper to the distal point. Occasional very well preserved 

 spines, however, show surface ornamentation, which consists of succes- 

 sive faint swellings, interrupted by constrictions, that give to the spine 

 a beaded appearance, as shown in the figure. This surface ornamenta- 

 tion was first observed by Mr Westergren when drawing the accompan}^- 

 ing figure. The dimensions of the spines are, average length 3 milli- 

 meters, maximum thickness at the base 0.4 of a millimeter, and from this 

 tapering to a somewhat blunt end at the distal terminus. 



The spines are frequently broken or reduced in size by erosion ; but 

 otherwise all have approximately the same length on both ambulacral 

 and interambulacral areas. On the interambulacra they are so much 

 more exposed that by far the greater part of the spines are short and 

 stubby from erosion. Only occasionally a long spine equalling the 

 length of those in the ambulacra is found ; but there are enough of these 

 to fully warrant the statement that the spines of both areas were of the 

 .same length. None of the spines of the interambulacra were seen show- 

 ing the bulgings described, but this is attributed solely to erosion, for 

 such ornate spines were only found in well protected areas. Besides the 

 specimen figured, another specimen of Melonites multiporus in the Museum 

 of Comparative Zoology (catalogue number 2996) shows spines. The 

 features exhibited do not diff'er from those just described. Spines have 

 also been observed on two other specimens. 



Hambach (18) has published a photographic figure of Melonites crassus, 



