SLIMONIA ACUMINATA. 105 



Genus 2. — Slimonia, Page. 1856. 

 Species 1.— SLIMONIA ACUMINATA :— Salter, sp, 1855. Plates XVII— XX. 



Himantopterus acuminatus, Salter. Quart. Journ. Geol. Soc. 1855, vol. xii, p. 29, 



fig. 4. 



maximus, lb. Id., p. 28, fig. 3. 



Slimonia acuminata, D. Page. Advanced Text-book, 1856, p. 135, fig. 3. 

 Himantopterus acuminatus, lb. Id., 2nd edition, 1859, p. 163, figs. a. b. 



lb. p. 159, fig. 2. 



Pterygotus acuminatus, Salter. Mem. Geol. Surv., Mon. I., 1859, p. 57, plates ii, 



xiii, figs. 1 — 4, xv, fig. 1. 

 Slimonia acuminata, H. Woodward, 1863. Intellectual Observer, vol. iv, p. 229, 



plate and woodcuts. 



Slimonia acuminata is the largest species found at Logan Water ; and its generic name 

 has been justly given to it in honour of Mr. Robert Slimori, who has, for more than 

 twenty years, laboured most assiduously, at Lesmahago, to perfect our knowledge of this 

 ancient and interesting order of Crustacea. 



If we compare the figures of specimens given on Plates XVII to XIX, accom- 

 panying this Monograph, with those published in 1859 by Messrs. Huxley and 

 Salter, we shall the better be able to understand and appreciate the vast amount of 

 additional information which we now possess, the result of Mr. Slimon's energetic 

 labours. 



Plate XVII represents the most perfect example known ; and will serve to convey a 

 very correct idea of the relative proportions and structure of Slimonia as compared with the 

 preceding genus Pterygotus. 



The specimen in this plate has its ventral aspect exposed, and, therefore, we do not see 

 the large trapezoidal carapace with its prominent marginal eyes (figured in Plates XVIII 

 and XIX) ; but we notice the elongated heart-shaped lip-plate or metastoma (m) in the 

 centre, covering the buccal cavity; the pair of minute and simple antennae (2, 2, and detached 

 fig. 3), which in this genus seem to take the place of the great chelate antennas seen in 

 Pterygotus (figured repeatedly in the plates which illustrate Parts I and II of this Mono- 

 graph) ; the three pairs of simple many-jointed and spinose endognaths (3, 4, 5, and 

 detached fig. 4) ; and the great swimming-feet or ectognaths (6, 6) with their broad basal 

 joints serving evidently as powerful jaws ; also the thoracic plate or operculum with its 



