Prof. H. J. Clark on Lucernaria. 19 



Fig. 6. Posterior maxilla. 



7. The last two segments of the thorax and the first of the abdomen, 



with one of its natator}' feet. 

 Figs. 8-18. Bacilli from the inner antennae of various Crustacea, magn. 

 90 diara. (except figs. 10, 12, and 16): s, stalk; a, outer, and 

 i, inner branch of the antenna ; v, blood-vessel. 



8. From a small Pagurus; 8 a, apex of one of the bacilli. 



9. From a small Prawn {Hippolyte 1); 9 a, apex more highly mag- 



nified. 



10. From My sis; magn. 45 diam. 



11. From Squilla. 



12. From the SphcEroma of the Baltic ; magn. unknown. 



13. From a young Bopyrus. 



14. 15. From two different species of Tanais. 



16. From Caprella; magn. 180 diam.; g, ganglion (?). 



17. From Gammarus. 



18. From a Copepod. 



III. — Lucernaria the Coenotype of Acalephcs. By Prof. Henry 

 James Clark, of Harvard University, Cambridge*. 



The present communication is a mere sketch of a most thorough 

 and exhausting anatomy oi Lucernaria, which I have illustrated by 

 numerous plates, and which I propose to publish in an extended 

 memoir, in connexion with some considerations upon the general 

 morphology and systematic relations of Acalephse. I have been 

 engaged during the whole of the past year upon the organical 

 and histological anatomy of this animal, in order to determine 

 what are its relations to Radiata in general, and to Acalephse in 

 particular. I have had abundant materials for study, inasmuch 

 as this species of Lucernaria is a very common inhabitant of our 

 shores, wherever the eel -grass {Zostera marina) grows. Almost 

 invariably Lucernaria is to be found upon the Zostera, and very 

 rarely upon any other plant. It may be obtained from the last 

 of August, when it is most frequently met with in a young state, 

 until the last of June, at which time the young ones of the 

 autumn season have developed to full-grown animals. In an 

 adult state it measures nearly an inch across the disk, exclusive 

 of the tentacles, and about the same in height. It varies in 

 colour from green, which is the most common tint, to deep 

 olive; from light yellow to reddish brown, or from light violet 

 to the deepest purple. In form it is octagonal, and most fre- 

 quently it so comports itself that the four sides opposite the 

 bifarious genitalia are shorter than those alternating with them ; 

 but frequently the same individual reverses the order of things, 

 and the latter become either as short as or even shorter than 

 the first. From this we infer that the specific differences, based 



* From Silliman's American Journal for May 1863. 



2* 



