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Note ox the Phyllosoma Stage of Ibacus Peronii, Leach. 



By William A. Haswell, M.A., B.Sc. 



I have had the opportunity lately of examining a specimen of 

 a glass-crab or Phyllosoma, which seems to be the young of the 

 highly specialised macrourous decapod Ibacus Peronii, and, as it 

 is somewhat rare to obtain these larvee at the stage when — though 

 still essentially Phyllosomce — they shew unmistakeably to what 

 species they belong, it is perhaps worthy of notice and description. 



The specimen, (which was obtained in Port Jackson and is in 

 Mr. Macleay's Collection) is thirteen lines in length and eight in 

 greatest breadth. Its cephalic shield is of quadrilateral form, 

 with the angles rounded off ; anteriorly it presents a deep, broad, 

 mesial excavation at the bottom of which the anterior cephalic 

 appendages are inserted, its antero -lateral angles reaching as far 

 forward as the penultimate joint of the peduncle of the internal 

 antenna} ; posteriorly it is terminated by a concave edge. Its 

 dorsal surface is covered with a number of somewhat irregular 

 radiating ruga3, has a deep longitudinal mesial depression along 

 the centre of which runs an irregular ridge, and presents on 

 each lateral half, about midway between the lateral margin and 

 the middle line, a sinuous ridge terminating anteriorly in a 

 flattened triangular-pointed process situated immediately behind 

 and external to the base of the outer antenna?. This shield has 

 still an essentially larval character ; it aj:>proximates, however, 

 towards that of the adult in the possession of the three ridges 

 above mentioned. The eye-peduncles are very long ; the second 

 j oint and the eye itself are compressed. The antennules equal 

 the eyes in length ; the segments of their peduncle are subequal ; 

 the outer flagellum is stouter and somewhat shorter than the 

 inner, which is about half as long as the peduncle. 



