980 MB. W. M. THOMSON ON A BRANCHIATE [Dec. 18, 



fig. 10 gives a drawing of an elytron from the middle of the left 

 side, which may be described as being typical of the rest. The 

 measurements of the transverse diameters are 9 mm. by 21 mm. 

 The general shape is transversely oval, but with a shallow sinus 

 in the elongated anterior border. All the elytra bear a number 

 of processes arranged around the external and posterior edges and 

 also on the neighbouring surface. The margins have further a 

 fringe of small hairs almost all round, which are visible in Plate LXI. 

 figs. 5, 6, and Plate LXII. figs. 9, 10. Plate LXII. fig. 9 is an 

 enlarged view of the part of fig. 10 between L. & e. The appear- 

 ance presented is curious, as two types of processes are seen. 

 The margin is produced into a number of very slender, round- 

 ended, hair-like processes (Plate LXII. fig. 9, 7i), and immediately 

 within these there is a series of stout, more or less cylindrical 

 spines, ending in a point and bearing conical thorn-like out- 

 growths just below the apex (Plate LXII. fig. 9, e). Occasionally 

 there are short and much more thorny processes (Plate LXII. 

 fig. 9, e l ). The bases of the spines are bluntly conical, and appear 

 from a surface view to be simply embedded in the elytra. The 

 spines arising from the flat surface further away from the margin 

 are much stouter, with fewer outgrowths, and arise from the 

 surface of the elytron by broad, star-like, spreading bases (PI. LXII. 

 fig. 9, st.b.). Many of them also have a little patch of pigment near 

 the tip and a small vesicle, for neither of which could any function 

 be guessed \ The surface of the elytra abounded in similar, but 

 smaller, star-like bases, bearing, however, only incipient processes. 

 The spines, especially the rooted ones, were more numerous on 

 the posterior elytra than on those situated further forwards. 



The first and last pairs differ in form from the remainder and 

 from one another. Of the first pair, the right member is almost 

 circular in outline ; the left is similar but has a wide notch in its 

 anterior border (Plate LXI. fig. 5, «.). The hinder margin of the 

 notch is covered by the edge of the elytron of the right side, 

 with which the anterior boundary of the notch forms an angle, 

 lying in the middle line, and evidently intended to allow freer 

 protrusion of the head or its appendages, which in preserved speci- 

 mens are seen below the notch (Plate LX. fig. 1). 



Each elytron of the last pair has a pear-shaped outline (Plate LXI. 

 fig. 6) ; the broader end is directed backwards and the narrower is 

 overlapped by the preceding elytron. The mesial edge, just in front 

 of the constriction between the two regions, is upturned, so as to 

 form a lip ; so that when the pair is in situ, an oval aperture is 

 formed, which overlies the hinder end of the dorsal subelytral 

 respiratory channel; this aperture is shown in Plate LX. fig. 1, 

 ex.ap. 



Parapodia. — Of these there are twenty-five typically constructed 

 pairs, each of which consists of neuropodium and notopodium, the 

 former being much the larger. The notopodium is a mere lobe 



1 It will be noted that this paper is simply an account of purely superficial 

 anatomy. 



