Most commonly this caterpillar is found on _Scrophularia_, but I have found it also on _Diplacus glutinosus_ and on a _Lonicera_, related to _L. Caprifolium_. The chrysalis is white with black and yellow dots. The butterfly is developed towards the end of April and is found until the end of June. There exists only one generation. The caterpillars grow very slowly through the summer. They are social and weave a kind of nest, in which they also hibernate. In spring their growth is quick enough, but they seem to be subject to much disease, and even in their natural state are frequently found half dried up. The butterfly also is often caught with crippled wings. 2. _M. Cooperi_, Behr, n. sp. Alae supra ut _M. Chalcedontis_, subtus inferiores sulphureae fasciis et maculis ordinariis fuscis, maculis fasciae submarginalis _fuscis concoloribus, neque ullo halone cicumdatae_. This species is very similar to _M. Chalcedon_, but the want of the yellowish halo around the lunulae of the brown band on the underside, is a very positive diagnostic character. The brown color of the bands also is always of the same somber hue as that of the underside of the forewings, and never of the fiery brick red that colors this fascia on the underside of _M. Chalcedon_, forming a perceptible contrast to the somber coloring of the underside of the forewings, which is the same in _M. Chalcedon_ and _M. Cooperi_. With all these well-marked differences, the two species look so much alike, that it would have been a long time before _M. Cooperi_ would have been recognized as a distinct species, if it had not been for the striking difference of its caterpillar, which was discovered by Mr. Lorquin near Clear Lake on a species of _Scrophularia_. This caterpillar is much more elongated than that of _Chalcedon_. It is nearly of the shape and coloration of that of the European _M. Artemis_, brimstone yellow, with a dorsal and a lateral black stripe. We were quite justified in expecting from such a caterpillar something strikingly different from the very common type of _Chalcedon_. But to our surprise our chrysalids gave us a series of crippled butterflies, which could scarcely be distinguished from _M. Chalcedon_. Since that time I have received a well-developed specimen through the kindness of Baron Koels, who caught it with several other insects on an excursion to Mount Tamal Pais. It is pretty certain that _M. Cooperi_ will be found in many other localities, as it is only its similarity to our most common vernal butterfly, the _M. Chalcedon_, that makes it escape our attention. 3. _M. Quino_, Behr, n. sp. _M. Chalcedonti_ similis sed antennae clava discolor, fusca nec concolor antennae reliquae aurantiacae.