observations on the Oribatidse. By A. D. Michael. 23 



dominated, and sometimes entirely hidden, by a lamellar and 

 tectiform expansion of its base, which advances forward, following 

 its declivity (that of the rostrum), and assuming a form more or 

 less triangular, according as the former is more or less angular, the 

 sides of which expansion are raised oblique projections, often pro- 

 longed beyond the front (of the expansion), and always terminated 

 by two setiform hairs. This apparatus, of the functions of which 

 1 am ignorant, but which I consider as a protecting organ, and to 

 which I have given the name of tectum, extends from the base of 

 one stigma to that of the others. The lower face of this organ, 

 where it is opposed to the upper surface of the cephalothorax, is 

 not always free in all species ; there even exist some in which it is 

 adherent all its length, and then the tectum is only distinguished 

 by its lateral wings, which in that case are usually more developed. 

 In other species this same tectum presents itself as two sub-parallel 

 blades, united by their inner edges, truncated and rounded anteriorly, 

 and through which the body of the cephalothorax may be seen ; 

 in this last case the tectum has not any lateral expansions. If I 

 notice these different modifications of the tectum it is because this 

 eminently variable appendage is the best specific distinction that 

 the Oribatidse of the first division present." 



Nicolet founds upon variations of the tectum, not only specific 

 distinctions, but even those of sub-families. He describes it in 

 several places, and evidently regards it as a chitinous shelf standing 

 free in the air in many species, except that its basal edge is attached 

 to the hinder part of the dorsal surface of the cephalothorax. This 

 shelf, he says, has turned-up lateral edges in most species ; these 

 he sometimes calls the raised borders and sometimes the lateral 

 wings of the tectum; for distinctness I shall give them a name, 

 and I speak of them as the lamellae. 



I have always had great difficulty in distinguishing the species 

 that Nicolet said had free tecta attached by their base only from 

 those which he said had tecta attached by their whole under surfaces 

 by this means of differentiation, but I presumed that Nicolet had 

 satisfied himself that there was such a thing as a detached tectum, 

 and it never struck me to doubt the existence of such an organ 

 until I came to dissect for the purposes of the Eay book ; had I 

 doubted it, and trusted to inspection of the living creature, or of 

 dead or mounted examples, I should probably have still considered 

 Nicolet to be right, for certainly in such species as Ce^heus tegeo- 

 cranus (vulgaris), which is the very type of Nicolet's free tecta, 

 it looks so very like what he described, that I not only should have 

 been, but was, deceived; when, however, I came to dissect the 

 organ away from the cephalothorax in this type species, I found, to 

 my amazement, that there was not anything to come. I then 

 passed a hair under the long projecting ends of the lamellae, and 



