312 Mr H. D. S. Goodsir on two New Species of Leachia. 



The strong claws with which the inferior antennae are armed, 

 seem also to be useful to the animal in the act of prehension. 



The genus Arcturus was constituted by Latreille for the 

 reception of Sabine's Idotea Bafini.* Westwood, in his paper 

 on the Arcturi, in the first volume of the Transactions of the 

 Entomological Society, included in this genus not only Sabine^s 

 Idotea Baffini^ but also Johnston's Leachia lacertosa, a species 

 differing from the former in the great length and development 

 of the fourth thoracic segment. Milne Edwards, in the Nouvelles 

 Suites a Buffon, following up Mr Westwood's arrangement, 

 divides the species of the genus Arcturus into two sets, the 

 one in which the fourth thoracic segment is not more deve- 

 loped than the others, and the other in which this segment is 

 elongated and provided with a pouch. The first set includes 

 only one species, that first described, — the Arcturus Baffini, 

 Westwood ; the second, the Arcturus longicornis^ Westwood, — ■ 

 Johnstone's Leachia lacertosa. Considering the highly deve- 

 loped fourth thoracic segment to be of generic value, I have 

 thought it right to restore Dr Johnstone's original genus, and 

 have therefore placed my two new species along with his L, 

 lacertosa in the same genus, retaining the genus Arcturus for 

 the reception of Sabine's original species. As the fourth 

 thoracic segment affords the characters of this genus, so the 

 antennae, and particularly the superior, exhibit the best marked 

 specific characters. These, and the sculpture of the surface 

 of the animals, have afforded sufficient characters for the three 

 species already described, and will, I have no doubt, serve to 

 distinguish any others which may occur. 



From an anatomical examination of L. lacertosa, I may state 

 the following details of structure in this very remarkable ge- 

 nus : — The nervous system consists of a supra-oesophageal 

 ganglion, from which the usual nerves of sense proceed, as 

 well as a cord on each side of the pharynx, to join the first 

 thoracic ganglion. At the base of each of the four ciliated 

 feet, a ganglion is situated. These ganglia are connected to 

 one another by double cords, and to three similar ganglia at 

 the bases of the three posterior feet by a long double cord, 

 which is situated immediately under the delicate transparent 



* Appendix to Captain Parry's Voyage, 



