268 BULLETIN OF THE 



of E. semilunaris the poriferous zone is much broader. It has also (taking 

 the same point of the test in specimens of the same size) larger tubercles, 

 and a greater number of large, glassy tubercles, while the miliaries are closely 

 crowded together. In E. cyclostomus, on the contrary, the primary tuber- 

 cles, as well as the glassy tubercles, are, proportionally, much smaller and 

 farther apart, the miliaries being more numerous. From the examination 

 of the alcoholic specimen from Florida, I could not come to any satis- 

 factory conclusion concerning the function of the glassy tubercles ; they are 

 not primary tubercles in the course of growth, as they are fully as large, 

 and the primary tubercles, when young, always appear at first as opaque 

 tubercles. They carry no special spines. On living specimens their func- 

 tion will probably be ascertained. Similar glassy tubercles often appear 

 on the edge of very young Clypeastroids (Stolonoclypus prostratus), which 

 disappear in older stages. Desor has given figures of the spines; but in 

 addition to these, the test is thickly covered with stout pedicellariae carried 

 upon moderate peduncles. The tentacles do not differ (as far as could be 

 judged from this alcoholic specimen, where they still were tolerably ex- 

 panded) from the tentacles of our ordinary Echini, having prominent 

 suckers. The tentacles retain the same structure from the mouth to the 

 apical system. On the lower surface, especially round the mouth and anal 

 system, the spines are longer and more slender than on the remaining por- 

 tions of test. The anal system will, I think, furnish good characters for the 

 determination of species, if we can judge from the striking differences the 

 arrangement of the plates of the anal system presents in the two thus far 

 examined. In the Pacific species the anal opening is more pear-shaped ; 

 the anus is placed near the blunt end, surrounded by a number of small 

 plates arranged concentrically round it, and extending as a narrow band of 

 small, slender, elongated plates between the single rows of large plates, 

 extending on each side along the other extremity of the anal system. This 

 row of large plates consists of five large plates, diminishing in size from the 

 centre of the row towards either extremity, and carry a fevf large tubercles 

 bearing spines. In the West India species, on the contrary, the anal sys- 

 tem is more elliptical, the anus being placed almost in the centre, sur- 

 rounded by a smaller number of small plates radiating from it irregularly. 

 The single rows are made up of four plates, leaving a triangular space 

 covered by small plates between them and the anus. The rest of the anal 

 system is covered by much larger polygonal plates than in the Pacific 

 species. The buccal membrane is covered by small quadrangular plates, 

 arranged in rows radiating from the mouth, diminishing in size towards the 

 opening of the mouth placed in the centre of the membrane. The absence 

 of teeth is fully confirmed by an examination of this specimen. The close 

 structural resemblance between the young of Echinolampadai and Echino- 



