I -ON THE SYNCARIDA. A HITHERTO UNDESCRIBED SYNTHETIC GROUP 

 OF EXTINCT MALACOSTRACOUS CRUSTACEA. PLS. I, II. 



BEAD APRIL 21, 1885. 



By a. S. Packaed. 



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 Wortheu, 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 

 E. D. Lacoe, esq., of Pittston, Pa., and .J. C. Carr, esq., of Morris, 111. 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 identitied, 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 tolei'ably accurate 

 account of the essential features of the group. 



The genus Acanthotelson was first proposed by Messrs. Meek and Wortheu, in 18G0, ' and the 

 species described as A. siimpsoni 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 autenuie, as well as in the forward direction of all its thoracic 

 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. stimpsotii (represented by fig. B, p. 510) 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 description, while embracing the more general characteristics of the group to 



' Proceedings Academy of Natural Sciences, Philadelphia. 



■^Amer. Journ. Sc.,2d ser., xlvi, 28, 1868. 



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