36 bulletin: museum of comparative zoology. 



ChEIRURUS DILATATUS, Sp. nov. 



Plate 4, fig. 1, 3. 



Sphaerexochus romingeri ? Hall, 28th Pi,ept. N. Y. state mus. nat. hist., 1877, 



doc. ed., pi. 32, f. 16. 

 Ceraurus (Cheirurus) niagarensis Hall, 28th Rept. N. Y. state mus. nat. hist., 



1879, mus. ed., p. 189, pi. 32, f. 16; 11th Ann. rept. Dept. geol. and nat. 



hist. Indiana, 1882, p. 335, pi. 34, f. 16, non pi. 33, f. 10. 



In the discussion of Cheirurus niagarensis (p. 30) frequent mention 

 has been made of the pygidium from Waldron which Hall figured. 

 This pygidium differs radically from the pygidia which have been 

 referred to Ch. niagarensis and Ch. welleri, in having broad, short 

 spines, each marked by a depressed line. This appearance of the 

 spines is probably due to crushing, in so far as the depressed line is 

 concerned, but the spines are decidedly shorter and broader than 

 those of the species previously described. 



Cheirurids seem to be rare at Waldron for a search through an ex- 

 tensive collection from that locality in the M. C. Z. has revealed only 

 one good cranidium, one poor one, and a pygidium. The best speci- 

 men is a fairly well-preserved cranidium, having much the general 

 appearance of Ch. niagarensis, only larger. On a closer examination 

 of the proportions, however, it is seen that this form is longer and 

 narrower than the typical specimens of Ch. niagarensis, and the 

 glabella makes up a larger proportion of the cephalon. In a specimen 

 of Ch. niagarensis from Rochester (M. C. Z. 625) the length is .57 of 

 the width and in the specimen from Waldron (M. C. Z. 628) it is .67. 

 In the first species the width of the frontal lobe of the glabella is less 

 than half the width of the cephalon (.46). In the latter specimen it 

 is somewhat more (.60). These appear, in figures, relatively small 

 differences, but when the areas involved are compared it is at once 

 seen that the glabella of the Waldron specimen is much larger than 

 that of the specimens of Ch. niagarensis. 



It is of course uncertain whether the pygidium described by Hall 

 is to be associated with the cranidium here discussed. It may belong 

 to the same species, and they are provisionally associated. The 

 cranidium is, however, made the holotype of the species, and the 

 pygidium a paratype. 



A large Cheirurus. The cranidium is dominated by the glabella, 

 whose frontal lobe is more than one half as wide as the total width 



