THE ATELEASPID^. 



363 



attachment, or for the exit of other organs of a similar nature, as for example 

 external gills. 



Fragments of what appear to be smaller appendages, covered with a thin 

 calcareous shell, have been found in the same deposits. They have a large, 

 flattened, terminal joint and two or three small segments, or joints, with 

 the surface raised into prominent peaks. (Fig. 241, F.) There is no other clue 

 to their origin. They may possibly represent the distal portion of the cephalic 

 arms of Thyestes or of some unknown arthropod. 



Ateleaspidae. — Head rounded, with heavy thickened margin; cornua trun- 

 cated. Entire body covered with small, five- or six-sided plates, ornamented with 

 bands or radiating lines, or canals, and with low rounded and polished tubercles 





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Fig. 242. — Ateleaspis. ^.Fragment, showing surface ornament, magnified; B, neural surface of head and 

 part of the trunk, showing parts of the " lateral line" ridges, marked by a narrow sinuous groove. At v.m. the shell 

 is absent, displaying a cast of the broad, flat hasmal margin, ornamented with prominent rounded tubercles. 

 (From Miguasha, Bay Chaleur, P. Q. About 2/3 natural size.) 



of varying size. (Fig. 200, B, 242, A.) No orbits. Sensory canals on trunk 

 and head, consisting of zig-zag, or interrupted grooves on a low narrow ridge. 

 Upper Silurian of England; Devonian of Miguasha, P. Q. Canada. 



I possess a fairly well preserved example of this very rare family, that was 

 obtained from the gray cliffs of Miguasha, and which probably represents a new 

 species. The greater part of the head is preserved and shows no trace of orbits. 

 (Fig. 242.) The haemal side of the thickened rim was broad, sharply marginate, 

 and studded with large tubercles. A lateral line groove extends well back onto the 

 flanks, and there are traces of a rostral and an anterior transverse line. The 

 trunk, as far as preserved, was covered with small five- or six-sided plates. 



This genus is of special importance, since it shows us an undoubted cephal- 



