64 MR. F. R. C. REED ON THE GENUS LICHAS.. [ Feb. 1902, 
LV. Tue Srrvcrvrs or tap Heap-Sarep. 
Homology of the Lobes and Furrows of the Glabella. 
It is doubtful whether the commonly-accepted nomenclature of 
the parts of the glabella in Lichas is based on a true conception 
of their homologous parts in other trilobites. It is essential to look 
into this question, in order to obtain a clear view of their morpho- 
logical equivalents before proceeding to attempt a natural grouping 
of the members of the family. 
In the first place, the disproportionate size of the so-called ‘first’ 
lateral lobes of the glabella is remarkable. The occasional presence 
of a more or less distinct furrow across these lobes, or of a notch on 
their inner side in various non-allied species, LZ. Pahleni, L. ornatus, 
L. gotlandicus, L. scutalis, etc., representing several of the above- 
mentioned subgenera or genera, suggests that these so-cailed ‘ first ’ 
lobes are in reality of a composite nature and consist of two fused 
lateral lobes. According to this hypothesis, the so-called ‘ second * 
lateral furrow is homologous with what is termed the ‘ third’ 
lateral furrow of other less-modified genera, and the so-called 
‘second’ lateral lobes correspond to the ‘third’ lateral lobes. 
On this hypothesis the segmentation of the glabella of Lichas 
is brought into correspondence with that of other trilobites. 
Dr. Beecher ' has arrived at the conclusicn that the trilobite-head 
consists of several fused somites, of which the first or anterior 
segment is represented by the hypostome ; the second by the paired 
eyes, free cheeks, and epistome; the third by the anterior lobe of 
the glabella and first antennz or antennules; the fourth by the 
second lobe of the glabella and the second pair of antennz; the 
fifth by the third lobe of the glabella and the mandibles ; the sixth 
by the fourth lobe of the glabella and the first maxille; and the 
seventh by the neck-lobe (=occipital lobe or ring) and the second 
pair of maxille. | 
‘The five annulations, or lobes, of the axis of the cranidium [=head-shield | 
since they primarily carry fulera for the attachment of muscles supporting or 
loving the appendages, could thus be interpreted in terms of the ventral 
structure, making the first lobe the antennulary. the second the antennary, the 
third the mandibular, the fourth the first maxillary, and the fifth the second 
maxillary.’ [Beecher, /oc. cit. | 
Following Beecher’s scheme, we must regard the anterior lateral 
portions of the so-called median or frontal lobe of the glahbella in 
Lichas as corresponding to the antennulary or true first lobe of the 
elabella. _ The so-called ‘first’ lateral lobes of Zichas would 
correspond to the fused antennary and mandibular lobes, the true 
second and third lobes of the glabella. The lateral lobes which 
are usually termed the ‘ middle’ or ‘second’ lateral lobes become 
homologous with the fourth or first maxillary; and the neck- or 
1 Amer. Journ. Sci. ser. 4, vol. iii (1897) pp. 95-97; see also Bernard, 
Quart. Journ. Geol. Sce. vol. li (1895) p. 352. 
