NO. 2 MIDDLE CAMBRIAN MEROSTOMATA 21 



Relations to pre-Camhrian Mcrostomes. — The fragmentary re- 

 mains that were described under the name of Beltina danai were 

 referred to the Merostomata/ and the genus was considered to be 

 more or less closely related to Eurypterus and Pterygotus. All the 

 original specimens are flattened in a calcareous shale and none of 

 them show definite surface m.arkings. In a collection made by Prof. 

 Stuart Weller in the Altyn limestone in the valley of Swift Current 

 Creek, Montana, the specimens are embedded in a very fine calcareo- 

 arenaceous matrix, and many of them show the convexity, and some, 

 the original surface markings. One of these (illustrated on pi. 7, 

 fig. 4), an abdominal segment, shows the convexity and general form 

 of the segment, and the surface is more or less roughened by what 

 appear to be depressed tubercles. 



Specimens collected from about the same horizon to the north in 

 British Colunibia, and embedded in a siliceous matrix, are more 

 flattened than those from the Altyn limestone, but they show certain 

 definite surface characters. Two of the specimens are illustrated 

 on pi. 7. Fig. 2 is a portion of a cephalo-thorax, with irregular 

 transverse ridges near the posterior margin and depressed tubercles 

 over other portions of the surface. An abdominal segment (fig. 3) 

 shows depressed tubercles not unlike those shown by the segment 

 from the Altyn limestone illustrated by fig. 4. 



The relations of this very ancient form to the Middle Cambrian 

 Merostomes described in this paper are very uncertain owing to 

 the fragmentary character of all the specimens of Beltina yet dis- 

 covered. Most of these fragments are quite similar to fragments 

 of Sidneyia inexpcctans where the latter is broken up and flattened 

 in the shale, but, as a whole, the form of all the parts of Beltina 

 thus far recognized indicates a closer relationship to the Eurypterida 

 than to the Sidneyidae. 



Class CRUSTACEA 



Sub-Class MEROSTOMATA (Dana) Woodward 



Order EURYPTERIDA 



Sub-Order LIMULAVA, new sub-order 



Body elongate, with a thin epidermal skeleton either smooth or 

 ornamented by lines or ridges. Cephalo-thorax with lateral or 

 marginal eyes, on the ventral side with five pairs of movable ap- 

 pendages ; mouth posterior to a large epistoma. 



^Bull. Geol. Soc. America, Vol. 10, 1899, p. 238. 



