Cylicin I (MW 74,788, deduced from sequence analysis), a basic protein (IEP 10.55) of the sperm head cytoskeleton with Mr 74,000 on SDS-PAGE, multiple band proteins with MW 58, 63, 69 and 74 kDa of calyx-associated polypeptides of bovine spermatozoa. Especially useful in discrimination of morphologi- cally altered "round-headed" spermatozoa