Type host: Microtus montanus.

Other hosts: Sciurus aberti; S. griseus; Tamias dorsalis; T. merriami; T. obscurus; Tamiasciurus hudsonicus; T. mearnsi.

Type locality: North America: USA, Arizona, N rim of the Grand Canyon, near the entrance to Grand Canyon National Park.

Other localities: Central America: Mexico, Baja California; North America: USA, California, New Mexico; Wisconsin.

Description of oocyst: Oocyst shape: elongate-ellipsoid; wall thickness: 1.5; layers: 1; outer layer colour: colourless; outer layer texture: smooth; micropyle: absent; OR: absent; PG: present; number of PGs: 1; PG shape: not given; PG L x W: not given; size: 32.5 x 19.3 (29-40 x 16-21); L/W ratio: 1.7 (1.4-2.0). Distinctive features of oocyst: none.

Description of sporocysts and sporozoites: Sporocyst shape: ovoid; size: 16 x 8; SB: present; SB L x W: not given; SB characteristics: blunt, cone-shaped (in drawing); SSB: absent; PSB: absent; SR: present; SR characteristics: large body in centre of the sporocyst, or dispersed; SR size: not given; SP: elongate and curved, with posterior RB. Distinctive features of the sporocyst: thin walled at the sides, but broadly thickened at 1 end and tapering to SB at the other end.

Material deposited: USNPC No. 87256 (phototype).

Remarks: Eimeria tamiasciuri was described by Levine et al. (1957) in Tamiasciurus hudsonicus. Since then, it has been reported in four genera, and seven species, including Microtus montanus in Arizona (Vance & Duszynksi, 1985).

References: Bullock (1959); Dorney (1962, 1963, 1966); Hill & Duszynski (1986); Levine et al. (1957); Mahrt & Chai (1970); Patrick & Wilson (1995); Soon & Dorney (1969); Vance & Duszynski (1985).