REPOET ON THE ACTINIARIA. 41 



Family, Paractid^e, Hertwig. 



Hexactinise, with numerous perfect septa, and with very contractile, moderately long 

 tentacles, which can be completely covered ; circular muscle very strong, mesodermal. 



The Paractidse form a family parallel to the Tealidse; they agi'ee with the latter in the 

 nature of the septa and the tentacles, but differ from them in the nature of the circular 

 muscle. The latter is enclosed in the mesoderm, and either lies close under the endoderm 

 or is forcibly separated from the epithelium by the secretion of abundant connective 

 tissue. In this famdy, as in the Tealidse, I include not merely the animals with 

 smooth body (genera Paractis and Dysactis), but also the papillose forms of the genera 

 Tealidium and Antholoha. 



Paractis, Milne-Edwards. 



Paractidae with smooth body surface, without papillae and without marginal spherules ; 

 tentacles nearly equal in length and in strength ; numerous longitudinal furrows of the 

 wall. 



The genus Paractis was founded by Milne-Edwards for Actinia3, of which the wall 

 has neither papillae nor marginal spherules, but can be drawn completely over the oral 

 disk and tentacles ; the tentacles are said, moreover, to be nearly ec|ual in length. 



Two forms of the Challenger material fulfilled these requirements ; they differed, how- 

 ever, in one very important point, as the circular muscle was endodermal in the one, meso- 

 dermal in the other. The former consequently belongs to the family of the Tealidae, 

 and for it I have composed the new name Leiotealia, whilst for the latter I have 

 retained the name Paractis. 



Paractis excavata, n. sp. (PI. I. fig. 6, PL XI. figs 13, 14). 



Wall with more than fifty longitudinal furrows, corresponding to the septa, oral disk 

 hollowed like a dish, with two rows of tentacles, the outer somewhat larger than the inner ; 

 tentacles thick waUed, with strong mesodermal muscles, which are present only on the 

 adaxial side at the base, but surround the tentacles on all sides towards the point. 



Habitat.— Station 300. December 17, 1875. Lat. 33° 42' S., long 78° 18' W. 

 Depth, 1375 fathoms. One specimen. 



Dimensions. — Diameter of the pedal disk, 2 '5 cm., of the extended oral disk, 6 cm. 

 Height of the wall in the contracted animal 2*5 cm., from the pedal disk to the margin of 

 the mouth 1 cm. 



Paractis excavata, which I describe as a new species, founded by me upon a single 

 specimen, is one of the most characteristic forms of the Challenger material, both as to 

 the shape of the body, and as to its finer structure. 



(ZOOL. CHALL, EXP. — PAET XV. — 1882.) P 6 



