568 Correspondence — Dr. Tbrnquist. 



usually found preserved. In the zone which is characterized by 

 this fossil, it occurs in the greatest profusion ; but owing to the 

 friability of the matrix, it is often difficult to protect the specimens 

 from destruction when kept in collections. Entire heads are not 

 rare, but they more commonly display only the central shield 

 between the facial sutures; other specimens present the same part, 

 but with the portion situated before the glabella and the ocular 

 ridges broken off. That the free cheeks are wanting in the 

 specimen figured by Linne, I have so much the less reason to 

 doubt, as I have in my own collection heads of ParaboKna quite 

 agreeing with the Linnean figure, but for the parts there visible 

 before the glabella. The free cheeks are indubitably absent for 

 the greater part, but a small portion of them behind the eyes 

 seems to be coherent with the fixed cheeks, since the outer margin 

 of the whole presents an uninterrupted curvature, just like that 

 seen in Linne's delineation. I cannot explain the cause of this 

 shape ; it may, perhaps, be due to the form of the inflected portion 

 of the free cheeks. However, a further examination of Linne's 

 drawing does not confirm Beecher's suggestion as to the nature of 

 the parts which Linne called antennae. If these were to be 

 interpreted as the thickened border between the facial sutures, 

 they ought not to have been pointed towards the end, nor to have 

 been so long as they are. These circumstances might, however, 

 be considered as depending upon carelessness of the draughtsman ; 

 and I should scarcely have mentioned them, if they had not been 

 combined with another detail, which cannot be accounted for as 

 due to such carelessness. Before the frontal lobe of the glabella 

 there is a smaller rounded lobe projecting between the pieces in 

 question, which is not only a little larger, but also more distinct in 

 the original figure than in Beecher's reproduction. The form of this 

 lobe seems to me to preclude the idea that we have before us the 

 thickened frontal margin. But if we imagine the foremost part of 

 the central shield before the glabella to be broken off, as is often 

 the case, there is another part which has just that position, quite 

 the same shape, and the same size as that lobe, viz. the anterior part 

 of the hypostome, or, more strictly speaking, of its central portion. 

 This organ is very often met with amongst the specimens imbedded 

 in the slates. From beneath this lobe the antennae appear springing 

 forth, and their bending can easily be imagined continued beneath 

 the hypostome, to their points ot attachment at the 6ides of the 

 same. 



Though I think this interpretation to be more in harmon}' with 

 the Linnean figure, I admit that the question is not so clear as 

 could be desired. But I believe I am fully justified in having 

 directed the attention of scientists to this early mention of 

 antennae in Trilobites, each palaeontologist being, of course, entitled 

 to attach just as much importance to it as his conviction demands. 



By several expressions in Beecher's paper, I feel called upon to 

 repeat from my earlier communication that " this reference to an 

 old" — and isolated — "observation^ can by no means abate anything 



