Study of the sounds found at the beginning and end of English words has shown that two groups of sounds with quite different patterns of distribution can be identified, and these two groups are those of vowel and consonant.
Could you paraphrase this sentence? I suspect that it would be something like:
Study of the sounds found at the beginning and end of English words has shown that two groups of sounds with quite different patterns of distribution can be identified, and these two groups are the groups of vowels and consonants.
Am I right? I don't understand why the author writes "those of vowel and consonant" instead of "those of vowels and consonants".