ELIOT : NUDIBRANCMS AND TECTIBRANCHS FROM INDO-PACIFIC. 299 



Bergh and von Jhering unite the Lophocercidte with the Lima- 

 pontiadse, Elysiadge, PhyllobranchidEe, and Hermseidai, in the group 

 Ascoglossa, which thus comprises animals of very different appear- 

 ance, and is regarded as forming a connecting link between the 

 Tectibranchiata and Nudibranchiata. As to the affinities of the 

 Lophocercidce with the Bullacea, there can be little doubt. The 

 external characters are very similar, and the main differences are 

 anatomical ; the digestive apparatus, the peculiar gillj and the absence 

 of an external seminal groove. But the recently-described genus 

 Neivnesia (E. A. Smith, 1902) bridges over the gap to a great extent, 

 inasmuch as it has a gill which appears to be intermediate between 

 the structures found in Bulla and the Lophocercidae, a uniseriate 

 though not ascoglossan raduLi, no jaws, and no stomach plates. 

 Some notes on this genus are appended to the present paper. Also, 

 it would appear from Bergh's investigations {Semper's Reisen, VII., iv., 

 iii., p. 249) that in Apliistrum there is an internal seminal duct and 

 no external groove. Most of the characters of the Lophocercidffi 

 (except the buccal crop and ascoglossan radula) are thus found in 

 some members of the Bullacea. 



Their affinities to the Elysiad;e and other families above mentioned 

 are at any rate less obvious, and are denied by Pelseneer.^ The most 

 recent writer on the subject, however, Bruel " is inclined to emphasize 

 these affinities.^ The most remarkable point of resemblance is the 

 striking similarity of the digestive organs, but this may be explicable 

 by similarity of diet. Nothing seems to be known of the food of the 

 Lophocercid?e, but some Ascoglossa live on the juices of seaweeds, 

 which are drawn up into the buccal crop and forced through the 

 alimentary tubes by the muscular contraction of this organ. No jaws 

 are required for this process, and the radula is only used for scratch- 

 ing the surface of the seaweed, which explains why the teeth are not 

 worn away. Now, it would appear that the nudibranchiate type is 

 the result of the larva breaking its shell and developing more or less 

 symmetrically, whereas the tectibranchiate type, in cases where the 

 shell is reduced or suppressed, is the result of the body growing over 

 the shell without altering the asymmetrical position of the gill and 

 other organs. If Lophocercus lost its shell and gill, so that the 

 pericardium and renal organ were spread on the top of the visceral 

 mass, it would become an animal not unlike Placobranchus. But 



1 " Recherches sur divers Opisthobranches," 1893. 



2 " Geschlechts- und Verdauungsorgane von Caliphylla iiiediterranea Halle," 1904. 



3 " Caliphylla steht, selbst unzweifelbar den Ascoglossen zugehurig, gleichvvohl der Gat- 

 tung Lobiger in eine Reihe von Charakteren die diese von jenen trennen (Lage der Niere, der 

 aorta im Schlundring, doppelte Tentakel-nerven, Bau des Kropfes und der Oesophagusdri'ise) so 

 ausserordentlich nahe dass ein natiirliches System auch den Lobiger aus der Ascoglossengruppe 

 nicht ausscheiden darf." /.c, p. 112. 



