98 Miscellaneous. 



These genera have been placed in very different positions, but 

 have generally been regarded as allied either to the Palaeoniscida? 

 or to the Pycnodonts. Prof. Young of Glasgow has proposed to 

 arrange them, with the latter, in a special suborder of Ganoids, 

 under the name of Lepidopleuridae — an arrangement which has met 

 with considerable acceptance. Dr. Traquair discusses the views 

 put forward by different authors, and then proceeds to a description 

 of the characters presented by the genera above mentioned, which 

 he shows to form a connected series, and proposes to include in a 

 distinct family, Platysomidae. He discusses at some length the 

 affinities of this family to the principal groups to which its members 

 have been thought to show relationships, and comes to the fol- 

 lowing conclusions : — 



" 1. That the Platysomidae are specialized forms which have, 

 if the doctrine of descent be true, been derived from the Palaeonis- 

 cidae. Their structure presents us simply with a modification of 

 the Palaeoniscoid type ; and wherever the Palseoniscidae are placed 

 in the system, thither the Platysomidae must follow. 



" 2. The resemblances between the Platysomidae and the Dape- 

 diidae and Pycnodontidae are mere resemblances of analogy and not 

 of real affinity. The Dapediidae are related not to the Palaeoniscidao 

 or Platysomidae, but to the other semiheterocercal Ganoids of the 

 Jurassic era {Lepidotus &c.) ; and the Pycnodonts are highly spe- 

 cialized forms, whose general affinities point in the same direction." 



Prof. Traquair regards the Palaeoniscidae and Platysomidae as 

 belonging to the Acipenseroid suborder of Ganoids. — Trans. Hoy. 

 Soc. Edinb. vol. xxix. pp. 343-391, pis. iii.-vi. 



On the Nervous System of Idothea entomon. 

 By M. E. Brandt. 



The nervous system of Idothea entomon presents fourteen gan- 

 glia — three cephalic ganglia, seven ganglia of the trunk, four 

 postabdominal ganglia. 



The only naturalist who has investigated the nervous system of 

 Idothea is H. Bathke * ; but his investigations are not exact. He 

 describes a single cephalic ganglion (he did not see the others) ; he 

 took the suboesophageal ganglion for the supraoesophageal, and he 

 does not correctly describe the nerves which issue from it. 



The supraoesophageal ganglion consists of six parts : it has two 

 median lobes, or the hemispheres, which give off two nerves for the 

 inner antennae ; two antennary lobes, which send off the nerves of 

 the outer antennae ; and two external or optic lobes, which bear 

 the nerves of the eyes. The oesophageal collar is short, very thick, 

 and furnishes two nerves for the labrum (nervi labii superioris). 

 The suboesophageal ganglion, which is small, furnishes three pairs 



* Neue Schriften der naturf. Ge*ellsch. in Danzig, 1820, p. 109 ; pi. iv, 

 fiff. 2. 



