On a Surviving Representative of the Lepidotrichidae (Thysanura)1

TRICHOLEPIDION gertschi was found under decaying hark and in rotten logs of Douglas-fir in the mesophytic forest of the northern California Coast Range. It is closely related to the Baltic amber Lepidothrix pilifera Menge, differing mainly by the presence of ocelli. T. gertschi (and, by implication, also L. pilifera ), compared to the remaining Thysanura (families Nicoletiidae and Lepismatidae), is characterized by a large number of primitive characters, such as lack of scales, combined with presence of hypodermal pigment; the hypognathous head with exceptionally well developed occipital and postoccipital sclerites; the presence of three pectinate appendages to the laciniae; weakly developed thoracic sternal plates; a large number of abdominal stylets and exsertile vesicles; urosternites composed of a large, transverse sternite and posteriorly situated coxopodites, both elements being well developed even on the eighth and ninth segments of the male; the lack of a proventriculus; and the presence of seven ovarioles in each ovary. Specialized characters probably shared by both genera of Lepidotrichidae are the five-segmented tarsi; the modified ovipositor adapted to insertion of eggs into vegetable tissue; a group of specialized setae on the dorsal surface of the base of the penis; a very large number of testicular follicles; and forwardly directed diverticula of the vasa deferentia functioning as sperm reservoirs. Pairing of mature sperms in Tricholepidion is considered as a condition precursory to the development of spermatophores as observed in the Nicoletiidae; the presence of sensory cones on the underside of the median caudal filament in the males is equally indicative of relationship with the Nicoletiidae. The Lepidotrichidae are considered to be the most archaic known dicondylous insects ; their relic character is further stressed by their actual geographic distribution.