INVERTEBRATES. 401 



this fossil, are real, and not simulative; since it would thus present mainly the 

 anterior structure (possibly even to the thoracic position of the branchige) of a 

 normal Amphipod, combined with the single pair of styliform, and five natatory 

 abdominal appendages of the Isopoda or Anisopoda. 



It must be evident, we think, that such an ensemble of characters as that 

 presented by our fossil, would exclude it from any known family of the Tetra- 

 decapoda; hence we can but regard it as the type of a new family, Acanthotel- 

 sonidse. 



Acanthotelson Stimpsoni, M. and W. 



PL 32, fig. 6, 6 a to 6/. 



Acanthotelson Stimpsoni, Meek and Worthen, March, 1865. Proceed. Acad. Nat. Sci., 

 Philad., p. 4.1. 



Linear or sublinear in form. Upper antennae at least as long 

 as the head and first five thoracic segments ; peduncle moder- 

 ately stout, rather longer than the head; first joint a little 

 longer and wider than the two others, which are of nearly 

 equal length ; flagellum slender and very minutely jointed ; 

 accessory appendage nearly or quite as long as the flagellum, 

 and like it, minutely jointed. Inferior antennae as long as the 

 head and seven thoracic segments; peduncle slightly longer, 

 but otherwise similar to that of the upper antennae ; flagellum 

 a little stouter and longer, but in other respects as in the upper 

 pair. Head, as seen in the (compressed) side view, subquad- 

 rangular, longer on the upper than the lower side, in conse- 

 quence of the obliquity of the anterior side ; eyes small, round, 

 placed just below the bases of the upper antennae. The (four- 

 teen) thoracic and abdominal segments distinct, and (excepting 

 the last one) of nearly equal length — a few of those nearest 

 the head being a little shorter than the others ; all diminishing 

 in depth (side view) from about the antepenultimate one for- 

 ward ; their anterior basal margins rounded ; posterior rectan- 

 gular or a little rounded. 



51 Oct. 3, 1SGG. 



