28 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The morphological interest of tliese and other observations of 

 Dr. Simroth's lies in the fact that von Ihering has divided the class of 

 Gastropoda into two phyla. One, that of the Arthrocochlides, he 

 derives from the Gephyrean-like forms (Amphineura) Chcetoderma and 

 Neomenia ; the other he calls the Platycochlides, and for these he finds 

 ancestors in the Dendroccelous Turbellaria. The central ganglion of 

 the first order (Protocochlides) of the Platycochlides is by that author 

 regarded as consisting of a single dorsal mass, from which arise two 

 pedal nerves, not connected one with the other. On the other hand, 

 the Placophora or Chitons, which are regarded as being intermediate 

 between the Amphineura and the Arthrocochlides, have the brain con- 

 sisting of an obscurely differentiated oesophageal ring. To this ring 

 there are attached, among others, two well- developed pedal nerve- 

 trunks, which are connected with one another by numerous transverse 

 commissures. This step-ladder system is obviously enough to be re- 

 cognized, as Simroth shows, in the Paludina, and it consequently 

 follows that this creature is one of the Arthrocochlides, were it not 

 possible that it had been obtained independently, and in consequence 

 of an adaptation. This latter view is supported by the comparatively 

 small number of commissures which are found in this Pulmonate ; but 

 to this it may be answered that there has been a fusion of the commis- 

 sures. Difiiculties such as these are insisted on by the author, who 

 comes to the conclusion that questions, but no answers, are suggested 

 by the study of the nervous system of this animal. Some answers 

 must, however, be found, and it is possible that great assistance may 

 be gained by an investigation of the anatomy of Neritina and Valvata, 

 for specimens of which the author makes an appeal. 



New Nudibranch.* — Dr. E. Bergh, our great authority on this 

 group, describes a beautiful nudibranch from the Mediterranean under 

 the name of Peltodoris atromaciilata Bgh. P. crucis (Oersted), from the 

 Antilles, formerly placed by Bergh in Discodoris, is now transferred 

 to the " new " genus. Both sj)ecies share with diverse Dorids and a 

 few other molluscs the curious property of parting with fragments 

 which break away from the margin of the mantle. 



Peltodoris Bgh. comes nearest to Discodoris. It has similar ten- 

 tacles and gills, a large prostate, an unarmed penis, and other charac- 

 ters of this genus, from which its smooth lip, destitute of armature, at 

 once distinguishes it. It is also of firmer consistence. 



But one specimen was available for dissection. Dr. Bergh figures 

 the entire animal (coloured in profile), its cephalic ganglia, ear-sac 

 with otocones, dental armature, and accessory genital apparatus. 



New Archaic Mollusc, I — Dr. A. A. W. Hubrecht describes a new 

 genus, to which he gives the name of Proneomenia (Sluiteri), and which, 

 he says, closely resembles Neomenia carinata in many of its anatomical 

 details. In external form it is cylindrical ; the anterior is thicker than 

 the posterior end ; the mouth and anus are on the ventral surface, and 

 the latter is continuous with the delicate ventro-median groove. The 



* MT. Zool. Stat. Neapel, ii. (18S0) pp, 222-32 (1 pi.), 

 t Zool. Auzeig., iii. (1880) pp. 589-90. 



