BY F. RATTE, ING. DES ARTS ET MANUF., PARIS. 97 



Acidaspis ruderalis, Cord. p. 733, pi. 37, fig. 32, length 30 mm. 



With all of these, including A . Dormitzeri, our specimen exhibits 

 some characters in common. Thus it resembles A. viinuta in 

 regard to the pygidium and in some degree the rounded outline of 

 the head ; while this species (A. minuta), difiei's from all others 

 mentioned by having three tubercles instead of one, on the pleural 

 ridges, not including one at the origin of the pleural spines. 



The pygidium does not seem to agree perfectly with that of any 

 of those mentioned ; besides it is smaller, being at the utmost one 

 eighth of the length, not including the spines; while in A. 

 Dormitzeri and A. minuta it is one seventh of the length, and in 

 the other more than that proportion. (1) 



The drawings being sufficiently enlarged to show all the visible 

 characters, I shall abstain from a lengthy descrijjtion, and insist 

 only on the principal features. 



The length of the head is less than one third of the whole lensrth 

 not including the spines. The median part of the glabella is 

 narrow, its width being a little less than one-fifth of the width of 

 the head. The distance between the false grooves which limit that 

 median part and the eye is a little more than the width of the 

 median part of the glabella, leaving ample room for the internal 

 triangle of the fixed cheek. This triangle includes on the specimen 

 four or five tubercles which are visible on both sides of the lateral 

 nodules of the glabella (those nodules, two on each side, are bounded 

 by the median, the posterior and the occipital furrows). In A. 

 Leonliardi, A. Hoernesi, A. (ji-einitziana, the above-mentioned 

 triangle is considerably reduced, and in L. Roemeri is completely 

 absent or replaced by a groove instead of an elongated nodule. 



(1) In fig. 22, pi. 38 of Barrande, the pygidium is certainly more than 

 one seventh, say one sixth of the length, but I quote Barrande's text p. 728, 

 " La tSte occupe un pen moins du tiers, et le pygidium un septieme de la 

 longueur totale." As the author says totale, it is possible that in this case 

 he included the spinal ornaments, although I doubt it. 

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