Mr. H. Giraud on the Structure of Pollen. 399 



" Magnus in hoc genere. Antennae corpore paullo breviores, 

 crassae, rufae ; articulis distinctis cylindricis. Caput rufum. 

 Thorax planus, depressus, margine utrinque antice posticeque 

 acutiusculo. Elytra striata. Pedes breves compressi." 



Sp. 4. Cato. puncticollis. Ferruginea, obscura ; prothorax ru- 

 gose punctatus, medio late depressus, linea mediana longitudinali 

 glabra : singuli elytri stria sex, exteriores indistinctce. (Corp. 

 long. '4 unc. ; lat. "1 unc.) 



Ferruginous, with very little gloss. Form very short and 

 stout, depressed, linear ; antennae hairy ; head sculpture al- 

 most precisely as in the two preceding species. The protho- 

 rax is coarsely punctured, and has a large but shallow dorsal 

 impression more rugosely punctured than the other parts, and 

 through the middle of this passes a raised longitudinal gla- 

 brous line. Each elytron has six equidistant striae, the two 

 nearest the suture are united at the base : these, as well as 

 the third and fourth, are clearly defined ; the fifth and sixth 

 are slight and indistinct. 



Inhabits North America. The Rev. F. W. Hope, to whom I am 

 indebted for the opportunity of describing this species, has labelled 

 it " rufus. Fab." He possessed a second specimen, very much 

 smaller, which he considers distinct. 



XLVI. — On the Existence of a Third Tunic, together with 

 certain other peculiarities in the Structure of Pollen. By 

 Herbert Giraud, F.B.S.E., Mem. Med. Soc. Edin. 

 [With a Plate.] 



In pursuing a series of observations on the structure and 

 functions of pollen, some points of anatomical peculiarity have 

 been presented to my notice which may not be wholly devoid 

 of interest. 



The existence of two membranes or tunics in the pollen- 

 grain has long since been satisfactorily determined by Brong- 

 niart, Amici, and Brown, and is proved in a most decisive 

 manner by the effects produced upon pollen by the action of 

 sulphuric acid; for when immersed in the dilute acid, the 

 pollen is seen to swell until suddenly a rupture takes place 

 in the outer tunic, upon which, however, neither the fovilla 



