46 A MONOGRAPH OF THE 



1. I. elegans, Leuck. Rose-coloured, freckled, the processes orange-yellow; anterior filaments 2; 



lateral filaments numerous, irregular, the posterior ones obtuse, lobular; dorsal filaments 

 5, — 3 on the median line, and 2 sub-lateral; branchial plumes 18 (the anterior and posterior 

 ones bifid) ; foot margined with yellow. Length li inch. PI. 27, figs. 1 — 4. 



2. I. Leachii, A. and H. White; filaments very long; anterior 4, lateral 6 on each side, the posterior 



ones bifid; dorsal filaments numerous, in 3 or 5 rows; branchial plumes 11 (the anterior 

 one bifid). Length 1 inch. PI. 27, fig. 5. 



Section 2. Centre of the back without filaments. 



Lingual spines next the centre large, recurved and strongly denticulated ; lateral spines 

 much hooked. Spinous collar incomplete, bilobed. 



3. I. aspersa, A. and H. Reddish or yellowish, freckled with orange and reddish-brown ; anterior 



filaments 4 (2 close to the base of each tentacle) of equal length, long ; lateral filaments 

 short, 2 or 3 on each side near the branchiae ; branchial plumes 10 (the anterior and pos- 

 terior ones bifid), short, equal, forming a circle. Length \ inch. PI. 26, and Appendix (12), p. iv. 



4. I. injEqualis, For. Gray, speckled with yellow and brown ; anterior filaments 4 (2 near the base of 



each tentacle), unequal, the exterior ones longest; lateral filaments short, 5 or 6 on each 

 side ; branchial plumes 9 (the anterior one bifid), slender, diminishing posteriorly. Length 

 1 inch. Appendix (13), p. v. 



5. I. pulchella, A. and H. Freckled with pale lilac; tentacles sub-clavate; anterior filaments 4, 



set on an expanded pallial ridge ; lateral filaments 5 or 6 on each side, the last large and 

 bifid; branchial plumes 11 (the anterior one bifid), rather small, diminishing posteriorly. 

 Length ~ inch. Appendix (14), p. v. 



6. I. quadricornis, Mont. Mottled brown and white ; anterior filaments 2 (1 near the base of 



each tentacle), long ; lateral filaments small, obscure ; branchial plumes 8 or 9. Length 

 § inch. Appendix (15), p. v. 



Fam. 2. TRITONIAD.E. Branchiae plumose or tufted, set along the sides of the back. Liver 

 entire, central. Skin without spicula. 



Genus 9. TRITONIA, Cuvier. 



Body sub-quadrilateral. Branchiae plumose or laminated, set on a pallial ridge along the 

 sides of the back. Tentacles 2, fasciculated, with plain sheaths. Veil digitated. Anus 

 lateral. Fam. 2, PI. 1. 



Tongue broad, with very numerous, simple or denticulated lateral spines : a tricuspid central spine, 

 and a plate on each side of it. Large corneous jaws. 



1. T. Hombergii, Cuv. Purplish-brown or flesh-coloured, strongly tuberculated; veil bilobed, with 



numerous small digitations; branchiae plumose, sub-foliaceous, forming a nearly continuous 

 line on each side. Length 3 to 6 inches. PI. 2. 



2. T. alba, A. and H. Transparent white with opaque white transverse markings, rather depressed, 



smooth, or very faintly tuberculated ; branchiae imperfectly bipinnate, 4 or 5 on each side, 

 with intermediate smaller ones, set on an expanded and waved pallial margin ; veil bilobed 

 with irregular digitations. Length § inch. Appendix (16), p. vi. 



