Herbert L. Hawkins — Studies on the Echinoidea. 441 



Fig. c shows the opposite side of the ossicle to that drawn in 

 Fig. a. It is not quite parallel to that side, hut makes a very acute 

 angle with it. Save for a slight median sulcus, increasing in depth 

 towards the narrow end, it is plain. It is very suggestive of the 

 external surface of the maxilla of Discoides (loc. cit., Fig. 2), but only 

 if the straight edge of the ossicle is regarded as the symphysial 

 margin instead of a cleavage line. 



It is difficult to imagine that this fragment can he other than 

 a part of a maxilla, and still more difficult to doubt that it belonged 

 to the specimen in which it was found. Other fragments include one 

 which suggests the existence of alar expansions like those of the 

 Clypeastroida (with a similarly reticulate character), and another 

 that is presumably part of a stirodont tooth. For the reason stated 

 above I prefer to leave all detailed discussion of these structures to 

 the future. The specimen figured is sufficient to indicate the grounds 

 for my belief that the lantern of C. albogalerus has been found at last. 



5. Summary. 



The perignathic girdle of Conulus albogalerus is shown to resemble 

 closely that of Discoides, with modifications due to the greater 

 degree of thickening of the interradial coronal plates and to the 

 massive character of the buccal plates. These are considered to be 

 the true plates of the buccal membrane, and to have been capable of 

 retraction into the deep sockets of the false ridges of the girdle. 

 The existence of a lantern is inferred as a result of arguments based 

 upon the known characters of the girdle and upon analogy with 

 related types. Certain imperfect ossicles found within the test of 

 a small specimen are considered to represent portions of the lantern ; 

 and one, here figured, seems clearly to be a fragmentary maxilla 

 similar in all essentials to that of Discoides, but differing in shape and 

 proportions. Further discussion of the presumed lantern is deferred 

 until better material is acquired. 



The next paper in this series will deal with the perignathic 

 structures of the Holectypoida as a whole, with a discussion of the 

 internal characters of the peristomes of some early Spatangoida. 



Fig. EXPLANATION OF PLATE XXVIII. 



1. Perignathic girdle of a gerontic specimen of C. albogalerus. xc. 6. All 



sutures except those at the sides of the processes are omitted. There is 

 a suture down the middle of each false ridge, but the median lines on the 

 true ridges represent the crests of carinas, not sutures. The outlines of 

 the various parts are slightly emphasized, but otherwise the figure is not 

 diagrammatic. 



2. Section along the axis 4, II, of the same specimen, x c. 6. 



3. Section along the same axis of a smaller specimen. x c. 9. The 



"platform" of the false ridge is indistinguishable. 



4. a, b, c. Fragment of presumed maxilla from the interior of a small 



specimen of C. albogalerus. x c. 14. a. ? Alveolar view, showing 

 ? distal hollows, ? symphysial surface (on the left), and ? dental slide (on 

 the right). b. Side view along the straight edge of the fragment. 

 c. ? Outer view, showing the shallow sulcus deepening towards the 

 narrow (? proximal) end. 



