mud shark vs spiny dogfish

mud shark

noun
  • Synonym of spiny dogfish 

  • A non-black person, usually a white woman, who has sexual relationships with black people, usually men. 

spiny dogfish

noun
  • Squalus acanthias, one of the best known of the dogfish which are members of the family Squalidae in the order Squaliformes 

How often have the words mud shark and spiny dogfish occurred in a corpus of books? (source: Google Ngram Viewer )