SALTER BRITISH NORTH AMERICAN CRUSTACEA. 77 



were portions of a concealed, three-jointed appendage, this analogy- 

 must have been received. But the more the specimen is studied, the 

 more clear it is that there are two pairs of appendages attached (one 

 pair to the sides, another near the tip) to the terminal joint. Squilla 

 and its allies, like all the higher Crustacea, have, of course, no ap- 

 pendages to the broad telson. And for the same reason, the affinity 

 of Diplostylus with the Macrura is out of the question. 



But when reference is made to the Isopoda, the resemblance is 

 much greater ; and none are better suited for comparison than 

 Sphasroma (fig. 7), which has a large, tuberculo-spinose, terminal 

 joint, and a two-jointed, palette-shaped style on each side. In 

 Sphceroma the appendages are higher up on the sides; in Serolis 

 they are nearer the apex. 



But in no case that I have yet seen or heard of, among Isopod 

 Crustaceans, are there two pairs of appendages to the last joint. 

 The Isopoda have all a single pair only*. 



Diplostylus Dawsoni, spec. nov. Fig. 6. 



The portion preserved consists only of five rings and the broad 

 telson ; and these together are -J of an inch long, and less than ± an 

 inch broad at the widest part. The telson is somewhat narrower 

 than the body-rings, broad above, and pointed behind, where it is 

 notched into three spines, the centre one very short, the two on 

 each side of it broad, and on their outer sides covering the attach- 

 ment of two small obovate palettes. These palettes are a little oblique, 

 narrower than their length, rounded at their posterior margin, and 

 striated distinctly. Outside these, and much higher up on the sides, 

 are a pair of broader notches, which give origin to a pair of small 

 palettes, ovate and not broader at their ends, and striated obliquely. 

 And above the insertion of these are a pair of broad, flat spines on 

 the surface of the tail-joint. 



The body-segments are transverse, the axis not much distinguished 

 from the short, pointed, recurved pleura ; with a narrow, articular 

 furrow, and strongly punctate on the exposed portions. The puncta- 

 tions (in the hinder segments only) are overhung by short plications : 

 such punctations are observable in many Isopod Crustaceans. 



Locality. Coal-measures of the Joggins, ISova Scotia, in a plant- 

 bed in the middle of the series. 



Having looked in vain for a similar pygidium among the large- 

 tailed Isopods, and consulted Mr. Spence Bate with a like result, he 

 referred me to a group of parasitic Amphipods (the Hyperina), among 

 which there are a few forms f (such as fig. 12) with tail-segments 

 coalesced and bearing appendages. These show a sufficient resem- 

 blance to warrant our referring Diplostylus provisionally to the 



* Lest it should be thought I had overlooked their occurrence, I may mention 

 that there is sometimes a pair of moveable spines at the extremity of the tail- 

 joint in Squilla, which might represent the terminal palette-like styles. Still 

 this would not account for the lateral appendages ; and I do not think there is 

 any real relation to Squilla. 



t Anchylomera, Typhis, Brachyscelus, Sec. 



