78 Annals Entomological Society of America  [Vol. XIV, 
the submentum. The suture in question, however, is rarely present in 
insects in general, and in such cases the posterior limits of the sub- 
mentum are demarked by an imaginary line drawn across from one 
gular pit “gp”’ of Fig. 15, to the other gular pit, or by a line drawn 
across from the base of one maxillary cardo ‘‘car”’ of Fig. 12, to the 
other, and corresponding in general to the line behind the label “‘sm”’ in 
Fig. 12. Dr. Craighead informs me that the submento-mental muscles 
labeled ‘‘11”’ in Figs. 11 and 14, which extend from the posterior border 
of the submental region to the posterior portion of the mental region, 
serve to demark the submental region “‘sm,”’ internally; and since the 
posterior line of attachment of these muscles corresponds in a general 
way to the posterior border of the submentum, they offer a valuable 
means of determining the homologues of the submental region when 
it is not clearly demarked externally. The most reliable method of 
determining the posterior limits of the submentum on the external 
surface of the head, however, is to draw an imaginary line between the 
bases of the cardines ‘‘car’’ of Figs. 24, 21, 20, 26, 31, 22, 9, 8, 7, etc., 
since it is not always possible to dissect a specimen (e. g., as is the case 
with dried material) in order to determine the origin and insertion of 
the muscles in question. 
In the insects shown in Figs. 21, 22, etc., the submental region 
contains two small plates, the swbmentales, ‘“‘sml,’’ situated at the base 
of the maxillary cardines ‘‘car.’”’ These submentals do not comprise 
the entire submental region, and in some insects, such as the one shown - 
in Fig. 20, the submentals are represented by the small areas labeled 
““sml’”’ alone. In the lepidopterous larva shown in Fig. 25, the areas 
labeled ‘‘sml’’ occupy a position at the bases of the maxillary cardines, 
“‘car,’’ as do the submentals of the insects referred to above; and the 
areas labeled ‘‘sml’’ in Fig. 25, as well as the ill-defined areas bearing 
the label ‘‘sml”’ in Fig. 29, may therefore be interpreted as representing 
the submentals of other insects. In the caterpillar shown in Fig. 28, 
the submentals ‘‘sml’’ are rather heavily chitinized and pigmented, 
and might be mistaken for the maxillary cardines, but the true cardo 
of the maxilla is the plate labeled ‘‘car” in Fig. 28. The submental 
region is membranous in some insects, such as those depicted in Figs. 
31, 77, etc., while in such insects as the beetle, shown in Fig. 17, ‘‘sm,”’ 
it is strongly chitinized and is deeply emarginate anteriorly. 
In the Neuropteron Nemoptera (Fig. 86) and in the Mecopteron 
Bittacus (Fig. 85) the principal part of the submentum ‘“‘sm”’ forms a 
portion of the slender column-like sclerite whose anterior region “‘mn”’ 
has been homologized with the mentum; and this tendency toward the 
formation of a column-like sclerite in the mental region is also found in 
some Diptera. Whether the submentum includes the entire plate bear- 
ing the label ‘“‘sm”’ in Figs. 10 and 6, or not, I cannot say; but it is 
very probable that the plate in question contains the gular region as 
well. It is also possible that the anterior, paler area bearing the label 
““sm’’ in Fig. 6, represents an anterior division of the submentum. 
The. mentum, “mn” of Figs. 5, 6, 7, 8, 9, 10; 238, 31, 12,:15,.77, etc:, 
is the region between the submentum, ‘“‘sm,”’ and the eulabium, or true 
