Hirudisomatid Millipeds 
107 
only inviolable characters involve the size and position of the penes 
on the second male coxae, which must be dissected and examined 
under a compound microscope. In his key to North American diplopod 
families, Hoffman (1990) placed the penes on the ventral coxal surface 
in the Hirudisomatidae and caudal to this podomere in the Polyzoniidae. 
To determine the correct family for Mexiconium, I had to examine 
the penes and compare their shape and location with these attributes 
in definite representatives of both families. As shown in figs. 3-4, 
the short, subconical penes of M. absidatum resemble those of O. 
bivirgata, and both are positioned caudoventrad on the coxae; in Poly- 
zonium rosalbum (Cope), however, the structures are longer, “bottle 
shaped,” and arise more dorsad (Fig. 5). Enghoff and Golovatch (1995) 
provide SEM photos of a European hirudisomatid and polyzoniid that 
also show the penes in these positions, so couplet 16a of Hoffman’s 
key (1990) should be amended to read “caudoventrad” as to the location 
of the penes in the Hirudisomatidae. 
Acronyms of sources of preserved study material are as follows: 
AMNH — American Museum of Natural History, New York, New 
York. 
CMN — Canadian Museum of Nature, Ottawa, Ontario, 
FSCA — Florida State Collection of Arthropods, Gainesville. 
NCSM — North Carolina State Museum of Natural Sciences, Raleigh. 
NMNH — National Museum of Natural History, Smithsonian Institution, 
Washington, DC. 
RBCM — Royal British Columbia Museum, Victoria. 
VMNH — Virginia Museum of Natural History, Martinsville. 
WAS — Private collection of William A. Shear, Hampden-Sydney, 
Virginia. 
Literature Review 
The history of the Hirudisomatidae in the New World begins 
with the proposal of Octoglena by Wood (1864) for O. bivirgata, a 
new species with fuscous stripes believed to inhabit the mountains 
of Georgia. He (Wood 1865) repeated these accounts and provided 
illustrations of the ventral and dorsal surfaces of the head. In the 
only other reference of the 19th century, Bollman (1893) included 
Octoglena in a key to North American myriapod genera. 
In the twentieth century, Cook (1904) proposed Hypozonium for 
H. anurum, a new species from Seattle, King County, Washington, 
and Chamberlin (1911) recorded it from Bremerton, Kitsap County. 
Cook and Loomis (1928) reiterated these records and transferred bivirgata 
into Polyzonium, thereby relegating Octoglena to the generic synonymy, 
