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Valmiki Ramayana, Kishkindha Kanda, Sarga 41 gives her name as Angaraka.

दक्षिणस्य समुद्रस्य मध्ये तस्य तु राक्षसी |
अंगारक इति विख्याता चायाम् आक्षिप्य भोजिनी || ४-४१-२६

"But a well-known demoness named Angaaraka is there in the midst of southern ocean who eats prey by grabbing its shadow when flying overhead. [4-41-26]

So, there seems to be two names of her as Angaraka and Simhika.

Valmiki Ramayana, Kishkindha Kanda, Sarga 41 gives her name as Angaraka.

दक्षिणस्य समुद्रस्य मध्ये तस्य तु राक्षसी |
अंगारक इति विख्याता चायाम् आक्षिप्य भोजिनी || ४-४१-२६

"But a well-known demoness named Angaaraka is there in the midst of southern ocean who eats prey by grabbing its shadow when flying overhead. [4-41-26]

So, there seems to be two names of her as Angaraka and Simhika.

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Her name was Simhika and her story is told in Valmiki Ramayana, Sundara Kanda, Sarga 1. When Lord Hanumana was flying over the Indian Ocean in search of Mata Sita, that demoness attracted his shadow for the purpose of eating him. Lord Hanumana with purpose felt in her mouth and then tore her internal organs and killed her.

प्लवमानं तु तं दृष्ट्वा सिंहिका नाम राक्षसी |
मनसा चिन्तयामास प्रवृद्धा कामरूपिणी || ५-१-१८२

A demoness by the name of Simhika with the power to assume desired form, saw Hanuma flying, increased in size and thought thus in her mind.

अद्य दीर्ग़्हस्य कालस्य भविष्याम्यहामाशिता |
इदं हि मे महत्सत्त्वं चिरस्य वशमागतम् || ५-१-१८३

"After a long time, this great animal came into my grasp. After long time, today I will enjoy my meal."

इति संचिन्त्य मनसा छायामस्य समाक्षिपत् |
छायायां गृह्यमाणायां चिन्तयामास वानरः || ५-१-१८४

Thinking thus in her mind, Simhika attracted His shadow. While the shadow was thus being grasped, Hanuma thought thus.

समाक्षिप्तोऽस्मि तरसा पञूकृतपराक्रमः |
प्रतिलोमेन वातेन महानौरिव सागरे || ५-१-१८५

"Like a great boat in the ocean with opposing winds, I am being pulled back forcefully, with disabled power."

तिर्यगूर्ध्वमधश्चैव वीक्षिमाणस्ततः कपिः |
ददर्श स महत्सत्त्वमुत्थितं लवणाम्भसि || ५-१-१८६

After that, Hanuma looking sideways, upwards and downwards, saw a big animal raised up in the salty ocean.

छाय्तद्धृष्ट्वा चिन्तयामास मारुतिर्विकृताननम् |
कपिराजेन कथितं सत्त्वमद्भुतदर्शनम् || ५-१-१८७

Hanuma saw that animal with a horrible face and thought: "This animal with a strange appearance, with great strength attracting shadow, is indeed the animal that had been told by Sugriva. There is no doubt in that."

आग्राहि महावीर्यं तदिदं नात्र संशयः |
स तां बुद्ध्वार्थतत्त्वेन सिंहिकां मतिमान्कपिः |
व्यवर्धत महाकायः प्रवृषीव वलाहकः || ५-१-१८८

That wise Hanuma recognizing that animal correctly as Simhika, increased His body greatly, like a cloud in rainy season.

तस्य सा कायमुद्वीक्ष्य वर्धमानं महाकपेः || ५-१-१८९
वक्त्रं प्रसारयामास पाताळान्तरसन्निभम् |

That Simhika seeing the growing body of the great monkey Hanuma, spread her mouth to be equal to the middle of Patala.

घनराजीव गर्जन्ती वानरं सम्भिद्रवत् || ५-१-१९०
स ददर्श ततस्तस्या विवृतं सुमहन्मुखम् |
कायमात्रं च मेधावी मर्माणि च महाकपिः || ५-१-१९१

Roaring like a dense cloud, she ran towards the Vanara. Then the wise Hanuma saw her opened very big mouth equal to His own body and also her internal organs.

स तस्या विवृते वक्त्रे वज्रसंहननः कपिः |
संक्षिप्य मुहुरात्मानं निष्पपात महाबलः || ५-१-१९२

That Hanuma with great strength and with a body equal to a diamond, repeatedly contracted His body and fell into her opened mouth.

आस्ये तस्या निमज्जन्तं ददृशुः सिद्धचारणाः |
ग्रस्यमानं यथा चन्द्रं पूर्णं पर्वणि राहुणा || ५-१-१९३

Siddhas and Charanas saw Hanuma sinking in her mouth, like the full moon on a full moon day being swallowed by Rahu.

ततस्तस्या नखैस्तीक्णैर्मर्माण्युत्कृत्य वानरः |
उत्पपाताथ वेगेन मनः संपातविक्रमः || ५-१-१९४

Then Hanuma rend her internal organs with His sharp nails and after that flew up with a speed equal to that of thought.

तां तु दृष्ट्वा च धऋत्या च दाक्षिण्येन निपात्य च |
स कपिप्रवरो वेगाद्ववृधे पुनरात्मवान् || ५-१-१९५

That wise Hanuma felling Simhika down with His vision, courage and ability, developed again by speed.

हृतहृत्सा हनुमता पपात विधुराम्भसि |
तां हतां वानरेणाशु पतितां वीक्ष्य सिंहिकाम् || ५-१-१९६
भूतान्याकाशचारीणी तमूचुः प्लवगोत्तमम् |

That Simhika with heart rend by Hanuma fell in water with sorrow. Seeing Simhika killed by Hanuma, creatures roaming in the sky spoke thus to that best among Vanaras.