NO. 13 LABIUM OF COLEOPTEROUS LARVAE ANDERSON 25 



terior arms (pi. 8, A, B, PT) arising from the posterior tentorial pits 

 are closely approximated at their bases, but as they proceed anteriorly 

 and dorsally, they diverge somewhat. Also, they are continued pos- 

 teriorly beyond the pits. On this posterior extension are attached the 

 ventral dilators of the pharynx, and on it also are inserted the ventral 

 muscles which extend from the prothorax into the head. United with 

 the distal ends of the posterior arms are the anterior tentorial arms 

 (pi. 8, B, AT). The dorsal arms (B, DT) originate from the anterior 

 arms and extend dorsally to the head wall. The lateral elements, each 

 consisting of a posterior, anterior, and dorsal arm, are not united 

 across the median line in Silpha. 



In Merinus laevis (C) the posterior arms {PT) have lost connec- 

 tion with the anterior arms. They are short and have broadened out 

 into rather flat plates, which, although close together in the midline, 

 are completely separate. On these arms are attached at least the ven- 

 tral adductors of the labium (pi. 5, C, 2adlb). 



Tenchroides (pi. 8, D) shows a condition very similar to that of 

 Merinus, the posterior arms {PT) being separate and not connected 

 with the anterior arms. 



The posterior tentorium of Sytichroa (E, F, PT) consists merely 

 of a transverse bar between the posterior tentorial pits and is some- 

 what concave ventrally. No projections or extensions, which might 

 indicate connection with the anterior arms are observable. On the 

 transverse bar are attached the ventral adductors of the labium. 



A somewhat similar case to the above is found in Ochrosidia villosa 

 (G, H) where the tentorium consists essentially of a bridge. It is. 

 however, not invaginated into the head but is continuous with the 

 lateral walls in such a manner as to form a smooth arch. From the 

 inner dorsal margin of this bar two extensions (G, H, PT) arise 

 which are evidently parts, at least, of the posterior tentorial arms. 

 On these are attached the strong adductor muscles of the maxillae 

 and the ventral adductors of the labium (pi. 6, E, 2adlb). 



The posterior tentorial apparatus of the staphylinid larva, Hesperus 

 baltimorensis (I, J), is made up of two Y-shaped structures, the base 

 of the Y being directed ventrally and connected with the posterior 

 tentorial pits. These lateral elements are completely separated. On 

 the base of each is attached its corresponding portion of the ventral 

 adductors of the labium. 



In Cicindela (K) the lateral elements of the posterior tentorium 

 have grown together at their bases, and there has resulted a flat trans- 

 verse plate extending nearly perpendicularly into the head. The inner 

 ends are slightly separated, which indicates that the tentorium, as it 



