13G JACKSON AND JAGGAR — STUDIES OF MELONITES MULTIPORVS. 



(ylark, of Johns Hopkins University ; Mr C. W. Johnson, of the Wagner 

 Free Institute, and Professor W. B. Scott, of Princeton.* Similar privi- 

 leges were extended to Mr Jaggar by Dr E. Newton, of the Museum of 

 Practical Geology, in Jermyn street, London. To my friend. Professor 

 Beecher, I am indebted for critical suggestions. Professor Whitfield and 

 Mr Johnson YQvy kindly had drawings made for me. 



Sincere thanks are due to Mr J. H. Emerton, of Boston, for the extreme 

 pains he took in making the drawings for the plates. Each individual 

 plate in a specimen was carefully scrutinized to ascertain its relative size 

 and angles, all peculiar plates, the position of columns, etcetera, were 

 measured, and all were drawn with great accuracy. No portions of 

 specimens as figured are restorations except in the cases where specially 

 stated and indicated by dotted lines or shading in the figures. 



Mr Jaggar, while working with me as a student in the Geological De- 

 partment of Harvard University, made the very important discovery of 

 the regular arrangement and progressive introduction of plates in the inter- 

 ambulacral area of Melonites muUiporus. His observations were based on 

 the specimen illustrated by plate 3, figure 12, and plate 4, figure 18, which 

 was at that time in the Student Paleontological Collection. Mr Jaggar 

 compared this arrangement with that of Ollgoporus danx, as shown in 

 Meek and Worthen's figure, introduced here as figure 34 of plate 6. He 

 also studied the spines of Melonites muliiporus. Mr Jaggar had not the 

 time nor the opportunity to carry the results of his observations further. 

 In London, at the Geological Museum in Jermyn street, he made draw- 

 ings of Palieechimts, which are reproduced in plate 7, figures 38 and 39. 

 I have carried on the studies of the interambulacrum of Melonites midti- 

 poras, extending it b}^ observations on other specimens. I have also 

 added the studies of the ambulacral area in this species. In the suc- 

 ceeding paper, "Studies of Pala3echinoidea," the researches begun in 

 Melonites midtiporas are extended to other species and genera. 



Robert Tracy Jackson. 



Description of Spines. 



The spines of Melonites midtiporus^'\ Norwood and Owen, have not 

 been previously described, though their general character has been sug- 

 gested by analogy to related species and genera and by the minute sur- 



* Many of the specimens described came from Ward's Natural Science Estabiisliment at Roches- 

 ter, New York. 



f As a matter of information worthy of record, it is stated where the types of Paleozoic echi- 

 noids described in this and the succeeding paper are deposited. The specimens of Melonites 

 multiporus figured in the Illinois Geological Survey, vol. ii, pages '227 and 228, are in the A. H. 

 Worthen collection, which is now in the University of Illinois, at Urbana, lllinos, as I am in- 

 formed by Mr William F. E. Gurley, state geologist of Illinois. These specimens and many types 

 are included in a published list of the Worthen collection. 



