490 A. Agassis — Eehinoneus Van Pixels . 



Art. XLYI. — On the Existence of Teeth and of a Lantern 

 in the Genus Eehinoneus Yan Phels ; by Alexander 

 Agassiz. (With Plate II.) 



While making some preparations of the teeth of Eehino- 

 neus for a report I am preparing on the specimens of the 

 genus collected by the " Albatross " in the tropical Pacific, 

 Mr. Magnus Westergren made the interesting discovery of the 

 presence of teeth and of a fully developed lantern (Plate II, 

 figs. 1,3) in young specimens of the West Indian species of the 

 genus E. semilunaris Lam. These young specimens (Plate II, 

 figs. 1, 2), measuring only 3"70 [imi and 4*25 mm in length, were 

 collected at Port San Antonio, Jamaica, by Professor Hubert 

 L. Clark. This is perhaps one of the most interesting recent 

 discoveries in the domain of echinology, considering the rela- 

 tionship hitherto recognized of Eehinoneus to the Atelosto- 

 mata. The presence of teeth would transfer them to the 

 vicinity of such types of the exocycla G-nathostomata as Holec- 

 typus, Discoidea, Pygaster (Echinoconidse) and more remotely 

 to the Conoclypidse. 



The demonstration of this interesting relationship would be 

 interesting in itself, but its great importance lies in the fact of 

 the disappearance of the masticatory apparatus at a very early 

 age. Young specimens of Eehinoneus measuring 5-l mm in 

 length, and but slightly larger than those in which teeth were 

 observed, have no teeth or lantern (Plate II, fig. 10) and noth- 

 ing is left of them but the presence of small auricles (Plate II, 

 fig. 4), so that in the older and adult stages of Eehinoneus its 

 relationship to the Spatangoids is in no way modified. 



The figures given on Plate II are sufficient to illustrate the 

 novel points in the structure of Eehinoneus. A more detailed 

 description will be given in a subsequent report on the genus. 

 Fig. 1, a profile figure of a young Eehinoneus measuring i-25 mm 

 in length, shows the position of the lantern with its compass 

 and teeth as well as the course of the oesophagus and of the 

 wide folds of the alimentary canal {i f and i n ) terminating in 

 the intestine leading to the anal system ; ia is a peculiar bag- 

 shape apparatus attached to the upper fold of the alimentary 

 canal, which is held in place by a line of mesenteries attached 

 to the test. 



Fig. 2, a transverse section of the test of a young specimen 

 of about the size of fig. 1, 3*70 mm in length, shows the actinal 

 floor of the test from above, with the anal system {an) and the 

 lantern in place, as well as the pyramid (py), the compass, c y 

 and the pentagonal muscular band of the upper part of the 

 lantern (pm). 



