526 PROF, C. H. o'dONOGHUE : BEPORT ON 
Certain authorities — e.g., Bergb (14 & 17), von Jhering (52 & 53) — recognise 
three sub-orders : name!}', the Tectibranchiata, the Nudibranchiata, and the 
Ascoglossa. The last-named sub-order is characterised inteT alia by the 
possession oi; a uniseriate radula with teeth o£ a special form which, when 
worn out, are not ejected, but retained in a sac lying at the base of the buccal 
apparatus [hence Saccoglossa von Jhering (52)]. The difScnlty in accepting 
this classification lies in the fact that the Ascoglossa undoubtedly contain 
two separate groups — (1) the Lophocercidse (^Lobiger and Lophocercus) ,vi\\ich 
show certain marked affinities with the Tectibranchs, so that by some 
authorities they are included with them, and (2) the Hermseidse, Phyllo- 
branchidaj, Placobranchidse, Elysiidfe, and Limapontiidee, which are 
undoubtedly more nearly related to the Nudibranchiata. Eliot (40), to 
overcome this, places the Lophocercidse with the Tectibranchs and the 
remaining families with the Nudibranchs. While this avoids one difficulty 
it creates another, for it does not sufficiently mark off these Ascoglossan 
forms, which deserve some recognition. Vayssiere (73) includes the 
Lophocercidai (Oxynoeidse) with the Tectibranchs and the remaining 
families he groups as a separate sub-order — the Ascoglossa, allied to the 
Nudibranchs. This restricts the application of the term Ascoglossa to the 
forms allied to the Nudibranchs, and excludes from it the Lophocercidse 
which are included under the older and original usage of the term and which 
are, of course, Ascoglossan. Pelseneer (65) has but two orders in the 
Opisthobranchs — the Tectibranchia and NudibrancHa. The latter he divides into 
four Tribes, of which the fourth (the Elysiomorpha) is identical with the 
Ascoglossa of Vayssiere. While agreeing that the Elysiomorpha constitute 
a group of forms related to the Nudibranchs, I cannot accept Pelseneer's 
view that they are highly specialised Eolidomorpha. Indeed, for a number 
of reasons that need not be entered into here, I am inclined to think that if 
there is any relationship between the Elysiomorpha and Eolidomorpha it is 
the reverse of this, and the former are to be regarded as the more primitive 
and not the derived group. 
The difficulty remains, and further work on the doubtful and transitional 
forms will be necessary before it can be satisfactorily settled. For the 
purpose of the present paper it is intended to adopt the classification set 
forth by Vayssiere in 1885 (73) and to divide the order Opisthobranchiata 
into three sub-orders — namely, the Tectibranchiata, the Ascoglossa, and the 
Nudibranchiata, using the term Ascoglossa in the restricted sense as identical 
with the Elysiomorpha of Pelseneer. 
Sub-order TECTIBRANCHIATA Cuvier, 1817. 
The Tectibranchs are characterised g(>norally by the possession of a lateral 
or dorso-lateral gill (ctenidiuni) on the right side, protected by a fold of the 
mantle ; usually a shell, internal or external ; a radula, whose used teeth are 
