AMERICAN ONISCOID DIPLOPODA OF THE ORDER MEROCHETA. By O. F. Cook, Custodian of Myriapoda. In July, 1890, I collected near Auburn, Alabama, a small oniscoid diplopod the affinities of which have been diflicnlt of deteiiniuation. It is quite similar to a sjjecies described from Arkansas by Bollmau as Sphcvriodesmus pudicus. The true geuus Sphcvriodesmus is, however, a vety different form, and among described genera the type under discussion approximates rather to Cyclodesmus, but otters diflerences apparently important and at least unique. Outside the Merocheta are to be found adaptations for securing safety by coiling up, conspicuously in the Onisconiorpha and in the family Striariidic of the C(j'locheta, where the first segment is produced in front into a hirge hood for the protection of the head. In the Onis-comori)ha the specialization for the habit referred to has reached its liigliest development, and the primitive condition of the ventral pro-tected i)art8 is evidence that this adaptation dates well back in the history of that order. In the liO segmented Merocheta the modifications necessary to render the habit of coiling up an effective means of defense have been exe-cuted in spite of greater initial difficulty, since the segments had, by the coalescence of all primitive sutures, become solid and inflexible chitinous rings. Moreover, this protective scheme seems to have been carried out, not once merely, but several times independently, for it appears from a comparative study of the five genera enumerated by Latzel us composing the subfamily Si)ha'riodesmia that these have noth-ing in common except this power of coiling closely. As conspicuous proof of the truth of this view, there need be noted only the fact that while some of the anterior segments are in each case enlarged to com-I)lete the armor of the closed animal, there have been at least three different inventions, if the expression may be permitted, to serve the same purpose. In Oniscodesmus and Cyrtodesmns the second segment is enlarged, in Cyclodesnius the third segment, and in Sphcvriodenvius the fourth and fifth, as may be better understood from reference to the plates. But even Oniscodesmus and Cyrtodesmn,s are widely distinct in all their characters, and the enlarge<l second segments do not resemble each other, showing that even where the same segment has been modi-tied the histories of the changes may have been entirely independent. Proceedings U. S. National Museum, Vol. XXI-No. 1154. 451
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