PORIFERA. II. 



Medd. nat. For. Kobenhavn for 1893.1894, 11) says that there is no reason to keep the genus, as in the 

 old genus Mycale (Esperclla olim) we have now exclusively anisochelse, now exclusively isochelee, and 

 sometimes a mixture of both, and as the difference between an isochela and an anisochela may be very 

 slight. I think, however, that there is good reason for keeping the genus, as the characteristic micro- 

 sclera in Mycale are anisochelae, and small isochelse seem to be of very rare occurrence in this genus. 

 Carter (1. c. 298) mentions this fact in a general way as occurring in some Mycale-species , among 

 which he only mentions M.plumosa Cart., aud Ridley and Dendy (Chall. Rep. XX, 65) state it with 

 regard to M. parishii Bow. in which species the small isochela is of a particular structure 1 ). 



With regard to the other objection made by Levin sen to the keeping of the genus it is to 

 be said that the anisochela;, to be sure, may approach isochelse as to form, but no species is known, 

 however, with regard to which there can be any doubt in this respect. The Mycale-species most 

 closely allied to Esperiopsis, and more particularly to the Esperiopsis-species with renierid skeletal 

 structure, is perhaps Mycale ovitlum O. S., in which some of the anisochelae may show only slight 

 difference as to the size of their ends, but the ends however are never of quite the same size. 



Another question is whether all the species for the present referred to Esperiopsis, are naturally 

 closely allied. The species show great difference, as well with regard to form as to skeletal structure; 

 also the combination of microsclera is varying to some degree, and rather many different forms may 

 occur. To get a general view I shall put together, as far as possible, the described species with a 

 statement of their microsclera; with regard to the species of Bower bank I follow, with a few excep- 

 tions, the interpretations of Topsent (Revue Biol, du Nord de la France, VII). 

 E. (Isodictya) Edwardii B Isochelae palmatae. 



- ( — ) Normani B — 



- ( 1 fucoruin Johust 



- ( — ) Alderi B 



- ( — ) scitula B 



- f — ) involuta B — 



- ( — J hispida B — 



? - (Halichondria) co/upressa B — 



? - / I Thompsoiii B 



- ( Antpliilectus) hispidula Ridley 



- Challengeri R. and D 



- profunda R. and D 



- anomala R. and D — 



- columnata Tops — 



- rigida Lambe — 



') Carter, as is well known, thought these small isochela? to be developmental phases of the anisochelae. He puts 

 forth this theory in 1874 (Ann. Mag. Nat. Hist., 4, XIV, 102), and here he figures for M. aegagropila Johnst. the typical aniso- 

 chela, as also some small bodies situated in cells, which bodies he interprets as isochelate developmental phases of the aniso- 

 chela. Levinsen (I.e. 9) has been of opinion that the question was here of small arcuate chelae. As there is, however, every 

 reason to suppose that Carter has really had before him M. aegagropila (he mentions one of Johnston's original specimens), 

 and as in this species no small isochelae are found, it is not possible to decide, what Carter has seen, and his figures are 

 not to be explained. Developmental phases of anisochelae thev cannot be, as those have a quite different appearance. 



