44 



the Hcsionides, it seems nevertheless to he properly referahle to the family of the Syllides, 

 among the Genera of which it appears to stand nearest to the Exogone 0rsted, especially 

 by reason of its wanting proper tentacular threads (cirri tentaculares) and by its simple not 

 beaded dorsal filaments. It presents however sufficient variations both from this and from 

 the other hitherto known forms of this family, for the establishment of a new Genus which 

 has received the name UmhcllisyUia on account of the remarkable large ciliated membrane 

 or screen situated at the posterior extremity of the head. 



The Umbellisyllis differs from the Exogone by the following peculiarities : 



1) The frontal lobes are not (as in the Exogone and Sylline Grube, Spermosyllis Clap, 

 and Sphwrosyllis Clap.) confused into one lobe, but, although united with each other at the base, 

 otherwise far apart from each other, as in the Syllis Sav. and many other genera of the Syl- 

 lides. They are in our animal indeed very small; nearly rudimentary, but yet distinctly to be 

 recognised by their being separated by a transversal furrow from the head itself. 



2) The 3 tentacles of the head are not .,placed in a transverse line in the furrow 

 which divides the frontal lobes from the head", which is according to Claparede the most 

 important Character of the genus Exogone. In the Umbellisyllis there are only 2 paired ten- 

 •tacles in or properly speaking close behind that furrow, but the third, (unpaired), is far be- 

 hind on the head or on the crown, in the middle between the posterior eyes, as in certain 

 species of Syllis (for inst. S. gracilis Grube) and in the Genus Spherosyllis Clap. 



3) Of the 4 eyes, the 2 posterior are larger than the anterior, while the contrary is 

 the case in the Exogone, and there are moreover immediately in front of the anterior eyes 

 a pair of extremely small black ocular points, as in the Syllides, Microsyllis, Sphserosyllis and 

 Odontosyllis. 



4) Underneath the head, or on the bucal segment, there are in the Umbellisyllis two 

 more tentacles, one on each side of the entrance to the mouth, which in form and size are 

 precisely similar to the tentacles of the head, and are hitherto only found in one single Syl- 

 lide, namely Autolytus roseus Clap. (Glanures zootomiques parmi les Annelides pg. 106) 

 although their position is here not more precisely indicated by Claparede, who nevertheless 

 in the explanation of the delineations calls them „bucal tentacles." 



.5) A specially characteristic mark of the Umbellisyllis is the peculiar, nearly semi- 

 lunar membrane or screen, situated at the posterior extremity of the head, to which screen 

 there is only found something similar in one single genus of the Syllides, namely, in the 

 analogous Sphserosyllis Clap., the 2 ciliated aliform appendages that appear in the saihe place. 



0) The dorsal filaments are not as in the Exogone small or „rudimentary" (Claparede), 

 but even a good deal longer than the tolerably long feet, and they are not situated on the 

 feet, but some distance above them on the sides of the body. The ventral filament, which 

 is quite small (in the Exogone Kefersteinii it is even wanting according to Claparede) is on 

 the contrary situated close tp the end of the foot. The pedal setaj differ from those of the 

 Exogone naidina, in which they are according to 0rsted sickle-shaped (seta; falcataj) or 



