530 DBS. H. C. SOBBY AND W. A. HEEDMA^^ ON THE 



does not extend mucli further north than the Channel. It does 

 not occur in Traustedt's list of the Simple Ascidians of the Danish 

 seas*. 



Ascidia mamillata has a very characteristic appearance, and is 

 easily recognized. Hellerf ga'^e a good general description of the 

 species in 1875 ; and, more recently, Julin % has made it the sub- 

 ject of one of his investigations into the nature of the dorsal 

 tubercle and neural gland. The arrangement of this " hypophy- 

 sary " system in the largest specimen is exactly as described by 

 Julin from an adult animal ; but in neither of the smaller speci- 

 mens is there any trace of a dorsal tubercle or terminal aperture 

 into the mouth of the branchial sac (PL X. fig. 4). In these 

 specimens there is also no peritubercular area. As noticed by 

 Heller, the anterior part of the dorsal lamina is double for a 

 considerable distance, nearly as far back as the nerve-ganglion 

 which is close to the atrial siphon (PI. X. fig. 3). The tentacles 

 are of three sizes (PI. X. fig. 2). In the moderately large speci- 

 men there are twenty large tentacles and twenty smaller, and 

 about the same number of very minute ones which alternate with 

 the others, but only occur in some of the spaces (PL X. fig. 2, tn"). 

 Opposite the end of the dorsal lamina two large tentacles occur 

 close together ; and opposite the end of the endostyle seven large 

 and seven smaller are placed alternately, but close, while the 

 minute ones are entirely absent in this region. 



Fam. 3. Ctkthiidj!]. 



Sttela geosstjlaeia, van Beneden. 



This very common species was found in abundance on dead 

 shells at various places in the English Channel. The specimens 

 are all of the squat, blister-like form, and are mostly of small 

 size. They occur attached to dead shells, stones, and the tests of 

 other Ascidians. 



There are several specimens from Cowes, Southampton, and the 

 Orwell, which belong to a well-marked variety. In shape they 

 difier greatly from the typical form, being elongated antero-pos- 

 teriorly. The specimen from Cowes is |- inch in length and only 

 I in its greatest breadth. The apertures are placed at the extre- 



* " Oversigt over de fra Danmark og dets nordlige Bilande kjendte Ascidiae 

 Simplices," Videnst. Meddel. Nat. For. Kjobenhavn, 1880. 



t " Untersuchungen iibei- die Tunicaten des Adriatischen Meeres," ii. Abth., 

 Denksch. der k. Akad. der Wissensch. Wien, Bd. xxxiv. 1875. 



\ " Eecherches sur rorganisation des Ascidies simples," part ii., Archives de 

 Biologic, vol. ii. 1881. 



