L—ON THE SYNCARIDA, A HITHERTO UNDESCRIBED SYNTHETIC GROUP 
OF EXTINCT MALACOSTRACOUS CRUSTACEA. PLS. I, IL 
READ APRIL 21, 1885. 
By A. §S. PACKARD. 
For a long time I have been desirous of examining into the relationship of the singular group of 
Carboniferous Crustacea represented by the genus Acanthotelson of Messrs. Meek and Worthen, as 
it has seemed to be a remarkable connecting link between the Edriophthalmata (or Tetradecapoda) 
and the Decapoda (in the older sense). An unexpected opportunity has been offered in a large 
series of specimens, which, without solicitation on my part, has been generously offered me by 
R. D. Lacoe, esq., of Pittston, Pa., and J. C. Carr, esq., of Morris, Ill. Mr. Lacoe’s collection was 
a very rich one, comprising over forty nodules, each containing a usually well-preserved Acantho- 
telson. Although additional specimens are much to be desired, especially such as may show the 
eyes and their nature, whether sessile or stalked, a point still unknown, the eyes not having been 
with certainty identified, and also to better show the nature of the abdominal appendages, it seems 
to us that enough characters have been preserved to allow us to present a tolerably accurate 
account of the essential features of the group. 
The genus Aeanthotelson was first proposed by Messrs. Meek and Worthen, in 1860,! and the 
species described as A. stimpsoni M. & W. A second species, A. eveni, was described by the same 
authors in 1868.% Additional facts were stated and figures given in the Report of the Geological 
Survey of Illinois, III, Paleontology, 1868. The specimens we possess enable us to amend and to 
add to their original descriptions; but in doing so we wish to bear witness to the care and ability 
displayed by the authors in the examination and illustrations of this form. The genus is referred 
with doubt by the authors to the Isopoda, who also refer to its resemblance to some of the lower’ 
types of macroural Decapods. They remark: “ From all the specimens of this genus now known 
it is evident that, in the nature of its anteunie, as well as in the forward direction of all its thoracie 
legs, and to some extent even in the nature of its caudal appendages, it differs from the Tetra- 
decapoda, and approaches some of the lower types of the macroural Decapoda. In the possession 
of seven distinct thoracic segments, without a carapax, however, as well as in the form of all its 
thoracic and abdominal segments, it agrees with the Tetradecapoda, particularly with the Isopoda, 
which have but one pair of the abdominal appendages styliform, instead of three, as in the 
Amphipoda. One specimen of A. stimpsoni (represented by fig. B, p. 549) also appears to show 
the eyes (marked I in the cut) to be sessile, though remarkably prominent. If they are sessile, this 
must be conclusive evidence that it must be a Tetradecapod. Until other examples, showing more 
clearly the nature of its eyes and some other parts, can be examined, we leave it provisionally 
where we first placed it with doubt, in the Isopod group of the Tetradecapoda.” (P. 550.) 
The following Sescup tion, while embracing the more general chee ous C a of the Sette to 
a Prceediige ade my of Natural Sciences, Philadelphia. 
2 Amer, Journ, Sc., 2d ser., xlvi, 28, 1868. 
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