Natyashastra
आदौ गुर्वक्षरं ?? अन्ते लघूनि चैव हि । त्र्यस्रः स खलु विज्ञेयस्तालश्चञ्चूपुटाश्रयः ॥ ११॥
That tala which begins with a long syllable and ends with two short syllables is to be known as Tryasra. It is based on the Capaputa pattern.
english translation
Adau gurvakSaraM ?? ante laghUni caiva hi । tryasraH sa khalu vijJeyastAlazcaJcUpuTAzrayaH ॥ 11॥
hk transliteration by Sanscript