NO. 3594 SARSIELLA — KORNICKER 5 



[of S. zostericola and S. americana] reported by Cushnian (1906) may 

 partly be the result of individual variation, or possibly the result of 

 comparing animals not of the same age," and, therefore, they con- 

 sidered S. americana to be a junior synonym of S. zostericola. Because 

 some of the differences between *S'. zostericola and S. tricostata disappear 

 when S. zostericola and S. americana are considered to be conspecific 

 and because some of Cushman's observations are obviously in error, 

 Kornicker and Wise (1962) considered S. tricostata. also to be a 

 junior synonym of S. zostericola. 



The present study of the ontogeny of S. zostericola shows that the 

 pre-adult female bears 2 ventral bristles on the 4th joint of the 1st 

 antenna, compared to 3 on the adult, and has the caudal process of 

 the carapace more posteriorly located than on the adult. The female 

 S. zostericola described by Cushman (1906, p. 365, pi. 28: figs. 15, 16) 

 bears only 2 bristles on the 4th joint of the 1st antenna, and the caudal 

 process is posterior, indicating that it is a pre-adult female. 



Since appendages of the holotype of S. americana are not available, 

 it is necessary to rely on the original description of the species in 

 which Cushman (1906) illustrated the 1st antenna (pi. 27: fig. 3), the 

 exopodite of the 2nd antenna (pi. 27: fig. 4), the caudal lamellae (pi. 

 27: fig. 6), and the mandible (pi. 27: fig. 5). Cushman reported only 

 5 bristles on the end joints of the 1st antenna. As other sarsiellids 

 have 9 bristles on the end joints (5th-8th), it seems likely that some 

 bristles were overlooked by Cushman. Cushman reported only 1 seta 

 on the ventral margin of the basale of the mandible of S. americana, 

 whereas S. zostericola has 5. The caudal lamellae and the exopo- 

 dites of the 2nd antenna of 8. americana and S. zostericola are 

 similar. 



Except for a possible difference in the number of bristles on the 

 ventral margin of the mandibular basale, ;S'. zostericola and S. ameri- 

 cana seem identical and, therefore, I concur with Kornicker and Wise 

 (1962) in considering S. americana a synonym of S. zostericola. 



I have compared the shells and appendages of adult specimens from 

 Massachusetts {S. zostericola) and California {S. tricostata) and I find 

 that the 2 populations cannot be distinguished, which confirms the 

 conclusion of Kornicker and Wise (1962) that S. tricostata and S. 

 zostericola are conspecific. Specimens of S. zostericola from Texas 

 could not be distinguished from those from Massachusetts and Cali- 

 fornia, and I can find no evidence of subspeciation in this ostracod. 



Because of the presence of instars in the collection from California, 

 it has been possible to study the ontogenetic development of the 

 species and to describe instars as well as the adults. 



