330 bulletin: museum of comparative zoology. 



and metathorax in a dorso-lateral position, and whose ventral attachment 

 is on the autero-ventro-lateral surface of the metathorax. In the ^jw^va 

 this fibre (Plate 3, Figure 7, I. prc.if. ms^pluj.) shortens very consider- 

 ably, but no more than would be expected from the growth of the 

 extensor alae magnus metathoracis during the same period. The dorsal 

 attachment of the extensor is just ventral to the ventral end of this 

 muscle, so that dorsal growth of the former, necessarily means a shorten- 

 ing of the latter. The attachments of this muscle in the imago (Plate 5, 

 Figure 11, I. pre. if. ms'phfj.) are, medianly, to the inferior process of the 

 mesophragma, and, laterally, just posterior to the metathoracic stigma. 



This muscle was not found by Straus-Dilrckheim in Melolontha, nor 

 by Luks in Dytiscus, nor was I able to find it in Colymbetes. It may 

 be present in some of these beetles, however, as it might easily be over- 

 looked in the dissections, on account of its small size. It is present 

 in both Synchroa and Bruchus, occupying the same position as in 

 Thymalus. 



Musculus lateralis mesofurcae. 



In the larva (Plate 1, Figure 4, l.ms^fur.') this muscle is found as 

 two nearly parallel fibres which extend from the antero-ventro-lateral 

 portion of the metathorax, anteriorly and ventrally, to the suture be- 

 tween the meso- and metathorax near the ventral attachment of the 

 musculus mesofurcae dorsalis. The two fibres fuse so as to be indis- 

 tinguishable in the pupa (Plate 3, Figure 7, I. nisfur.), maintaining, how- 

 ever, a closely similar position. The attachments in the imago (Plate 5, 

 Figure 11, I. msfur.) are, medianly, to the tip of the mesofurca (7m'/ur.), 

 and, laterally, just posterior and ventral to the metathoracic stigma 

 (sfg. mfthx.). 



This muscle is not mentioned by either Straus-DUrckheira or Luks. 

 It also did not show in my dissection of Colymbetes, nor could it be 

 found in the sections of Bruchus. It is present in Synchroa, however, 

 extending from the mesofurca to the lateral wall of the metathorax as in 

 Thymalus. 



Depressor tevgi. 

 (Abaisseur du iergum of Straus-DUrckheim.) 



In the larva the depressor tergi (Plate 1, Figure 3, dep. trg.) is a sin- 

 gle fibre, extending dorso-ventrally along the suture between the meta- 

 thorax and the first abdominal somite. In the young pupa (Plate 3, 

 Figure 7, dep. trg.) there is a very evident bend both in this muscle and 



