124 W. I). Matthew — Antennae of Triarthrus. 



belonging to Prof. A. H. Chester, shows an antenna with the 

 end coiled spirally inwards. 



Besides these, there are shown in several of the specimens, 

 other appendages, some of which may be branchial in their 

 character, and others walking or swimming legs. In fig. 1 the 

 side of the head-shield has been broken away, exposing the 

 appendages apparently of three cephalic segments. These are 

 of two kinds, one of which is a narrow, jointed cylindrical 

 leg, and the other is thin, broad and leafy, with what seems to 

 be a comb-like structure similar to the gills of many Crustacea. 

 These branchiae, if so they be, depend from a narrow, thick- 

 ened anterior edge or limb ; they seem to correspond with two 

 of the three legs shown in the specimen, and to overlie them. 

 By analogy with Mr. Walcott's determinations, they are prob- 

 ably attached to the basal joint of the legs. 



In figs. 2, 3 and 6 are shown the ends of appendages which 

 projected from under the carapace, and seem to belong to the 

 thoracic region. These are likewise of two kinds, one flat, 

 furrowed, and showing a series of oblique parallel lines all 

 along it (see figs. 2, 2a, 3 and 4) ; and the other a strong taper- 

 ing leg, with three cylindrical or slightly flaring joints visible 

 (see figs. 2, 2a, 3, 5 and 6). The first may be a branchial 

 appendage ; it is flattened and appears in one case to broaden 

 out into a small paddle at the tip (though this may very likely 

 be deceptive) ; it has a sharp ridge and narrow furrow along 

 the anterior edge, and behind that the series of lines or comb- 

 like structure, which may be due to the remains of hairs or 

 gill structure on the limb. 



Figure 4 shows a series of appendages of both kinds, but 

 very poorly preserved. In figure 7 the projecting appendages 

 of the tail-piece are shown, and it may be seen that apparently 

 several, and perhaps all of the pygidial limbs are anchylosed, 

 so as to make a rounded flap, which in shape, though not in 

 structure, reminds one of the telson of a crayfish, and may 

 possibly have served somewhat the same purposes. 



The conclusions as to the nature of these appendages are 

 only provisional, and may be much changed by further dis- 

 coveries. They are not nearly as well preserved as the anten- 

 nae, nor in so considerable a number of specimens ; for besides 

 those figured, there are but two or three others which show 

 them at all, and those only in traces. The shape and structure 

 of the supposed branchiae, in particular, are very hard to dis- 

 tinguish; the figures given, however, represent as far as I can 

 see the actual outlines preserved. 



It will be seen that the structure of Triarthrus must have 

 differed not a little from that described by Mr. Walcott in 

 Calymene and Ceraurus. The presence of antennae, the pecu- 



