Vol. XXvii] ENTOMOLOGICAL NEWS. =57 



A New Descriptive Formula. 



By C. W. WOODWORTH, University of California, Berkeley, 



Calif. 



The writer has used in his classes for a number of years 

 certain methods for pointing out features of structure which 

 are very evident to the eye, but not easily expressed in simple 

 descriptions. 



One of these, which has been particularly helpful, is pre- 

 sented below. It consists in the use of shape formulae for 

 Hemiptera and Coleoptera. It has been found possible to thus 

 describe the structure in question so well that a student can 

 reproduce a recognizable picture from a line of numbers with 

 more accuracy in detail than found in many published illustra- 

 tions. 



The plan in these formulae has been to determine the meas- 

 urements a careful artist would make when laying out a draw- 

 ing and by always arranging the numbers in the same order 

 avoid the necessity of specifying what each measurement in- 

 dicated. Instead of making these measurements in fractions 

 of inches or millimeters, it was found better to use a portion 

 of the body as a unit and the dimension finally adopted was a 

 tenth of the length of the prothorax. This proved sufficiently 

 accurate for the purpose and not too minute. 



The sequence of taking the measurements is indicated on the 

 accompanying figure. The head measurements are taken from 

 measurements from the front edge of the thorax, and the 

 thoracic and abdominal measurements from the hind edge of 

 the thorax. The widths 6, 8, 10, 11, 12 and 13 are measured 

 from side to side, the others along the middle line parallel 

 with the axis of the part. Where the axis of the body bends 

 there should be added (14) the number of degrees bend at 

 the head and thorax articulation and (15) the angle at the 

 pro- and mesothorax articulation. When the pygidium is want- 

 ing 3 and 4 would be given as the same size and 13 would 

 read o, and if the thorax is widest at the hind angles then 7 

 would be o and must be included to avoid the necessity of ex- 

 plaining its absence. The formulae for the bug and beetle 



