CRUSTACEA. II 



HOMALONOTUS \' A\ I \ i:\ll. 

 PLATE V B, FIGS. I, -•. 



Homalonotus Vanuxemi, Hall. Palaeontology N. Y., vol. iii, p. 352, pi. Ixxiii, figs. 9-14. 1859 



This species was described from very meager material consisting of detached 

 pygidia and a fragment of the thorax. Although it has proven to be a fossil 



of rare occurrence, more complete specimens have since been obtained, which 

 make the introduction of the species in this place important both for the pur- 

 pose of extending the knowledge of its characters and of comparison with the 

 Devonian Homalonoti. The very large fragment here figured consists of the 

 pygidium and eleven segments of the thorax, the latter part being considerably 

 weathered on the left side and over the dorsum. It was obtained from a 

 quarry in the Lower Helderberg limestone at Kingston, Ulster county, and 

 is so preserved as to retain its normal convexity. This specimen shows that 

 the species approximates very closely Homalonotus delphinocephalus, Green, differ- 

 ing from the latter, however, in the features pointed out in the original descrip- 

 tion, namely, the greater number of annulations in the pygidium ; the former 

 having upon the axis eleven or twelve, including the articulating ring, the latter 

 nine or ten ; and upon the pleura? the former ten and the latter eight. The 

 pleural slopes of H. Vanuxemi appear also to have been considerably broader. 

 The cephalon, which is restored in the figure from a fragment (the only example 

 yet observed) taken from the limestone at Port Jervis, Orange county, is con- 

 siderably produced at the anterior extremity, even more than in H. delphinocephalus 

 or H. Dekayi. Just in front of the glabella is a, gentle and broad depression, 

 giving to the frontal prolongation a shovel-shaped surface. Tin' glabella is 

 generally smooth, and regularly convex, unlike that of the Niagara species, 

 which often shows a lobate character. That the Lower Helderberg species 

 attained very considerable size is shown by the restoration of the missing parts 

 of the figured specimen, as given upon the plate, indicating that the animal 

 reached a length of 275 mm., or eleven inches. 



