Coleopterological Notices, V. 3*11 



THINUSA n. gen. 



Body very narrow, parallel and linear, thick, opaque. Head 

 wider than long, slightly narrower than the prothorax ; sides par- 

 allel toward base, the latter very broad and inserted within the 

 prothorax ; eyes moderate ; labrum truncate. Antennae short, 

 moderately iucrassate, the second joint as long as the next two. 

 Mentum transverse, trapezoidal, truncate. Maxillary palpi normal, 

 the second joint shorter than the third ; labial three-jointed, the first 

 joint apparently longer than the second. Infralateral ridge obso- 

 lete. Prothorax strongly narrowed from near the apex to the base; 

 hypomera feebly inflexed, rather narrow but extending almost to 

 the apex ; base of the pronotum superposed over the base of the 

 elytra and broadly, feebly arched throughout the width. Elytra 

 very short. Abdomen long, linear, as wide as the elytra, the first 

 four segments impressed at base; fifth much longer than the fourth; 

 sixth visible. Cox« very large, the anterior extremely so; middle 

 cavities deep, distinctly limited, approaching extremely close to the 

 posterior margin. Metasternum very short, the side-pieces narrow, 

 parallel to the oblique edge of the elytra. Legs stout ; tibiae very 

 short, the anterior and middle spinulose externally ; tarsi short, 

 stout, the first four joints of the posterior subequal. 



This genus is allied to Phytosus but distinguished at once by its 

 very short elytra and extremely abbreviated metasternum. From 

 Actosus it may be known by the much narrower and more lineate 

 body, the narrower met-episterna, which are perfectly parallel to 

 the edge of the elytra, and by the much less developed met-epimera. 

 The single species is common about San Francisco. 



T. maritiiua Csy.— Bull. Cal. Acad. Sci., I, 1885, p. 312 (Phytosus). 



The European Actosus halticus must form part of the genus 

 Phytosus, or else be regarded as the type of a new genus allied 

 to Thinusa ; it is altogether generically distinct from Ac. nigriven- 

 tris — the type of Actosus — in its narrow parallel metasternal side- 

 pieces, these being very strongly triangular in nigriventris. All 

 of these genera differ, in addition, from Thinusa, in having the 

 infralateral carina of the head distinct toward base and the hypo- 

 mera much more dilated behind. 



