It's likely you're thinking of the White English Terrier, which is a breed that did go extinct. This breed was a smaller, more refined version of the modern Bull Terrier, and it was developed in England during the 19th century. The White English Terrier was popular for a time, but it eventually fell out of favor and was discontinued.
The modern Bull Terrier is a direct descendant of the White English Terrier and still retains many of its physical characteristics, including its white coat. However, the White English Terrier as a distinct breed no longer exists.