176 THE OEDEH OF COLEOPTERA. 



aud other plants of the composite family, but most of the American 

 species are found on different species of convol\Tilus, especially the 

 morning-glory and the sweet-potatoe, both of which belong to this genus 

 of plants. The leaves of these plants are often riddled with holes, and 

 seriously injured by these insects. 



It is in this family that the habit of the larvse of covering themselves 

 with their own excrement is most conspicuous and universal. Other 

 larv?e fCrioceris and BlepharidaJ, which have this habit, void their ex- 

 crement directly upon their backs, but the larvte of Cassida support 

 their excrement on a long forked process which issues from the body 

 Just above the anal aperture, and is directed forwards over the body 

 like a parasol. The object of this singular habit is supposed to be to 

 protect the insects either from birds and other natural enemies, or from 

 the direct rays of the sun. The former is probably the true explanatit)n. 

 That it can not be the latter, seems to be proved by the practice of 

 most of these larvae of feeding upon the under side of the leaves where 

 the direct rays of the sun cannot reach them. Mr. Eiley has stated 

 this to be the habit of the larvse of many of the Cassidides, and I have 

 observed the same to be true of the larvae of Blepharida rhois. 



The Cassidides present four well marked genera as follows : 



A. Head prominent, visible ; size below medium ; color blue Porphyraspis. 



A A. Head partially visible ; prosternum advanced ; size large ; red spotted with black. .Chelymorpha. 

 A A A. Head completely concealed. 



B. Body oblong oval, convex ; size large ; color dull greenish brown Physonota. 



B B. Body oval or orbicular, moderately convex or depressed ; size about medium ; colors 



•various Cassida. 



Porphyraspis, Boheman, meaning & purple shield, is founded upon the 

 Cassida cyanea of Say, found in the Southern States. Chelymorpha, 

 Chev., signifies literally tortoise shape. It has for its type the C. cassidea, 

 Fabr., subsequently named cribraria, by the same author. It is also the 

 C. argus of Herbst. It is about four- tenths of an inch loug, of an ob- 

 long oval, convex form, brick-red, with four or six black dots on the 

 thorax, aud six on each elytron. The larva is said to feed upon the 

 milkweed. Physonota, Boh., meaning sioollen or convex hacJc, contains 

 the P. imipunctata. Say, of about the same form and size as the preced- 

 ing species, but the head is completely hidden under the anterior 

 margin of the thorax. It is of a dull greenish or yellowish-brown color, 

 with one, three, or five black dots on the thorax. Cassida "has been di- 

 vided into two sub-genera, Cassida proper having the antennse not 

 longer than the thorax, and usually of a sub-convex, oval form ; and 

 Copiocycla, with the antennae longer than the thorax,, and usually of an 

 orbicular and depressed form. The species which occur in this section 

 of country may be tabulated as follows : 



