In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Pharmacological studies on a new dihydrothienopyridine calcium antagonist , S - 312 - d .
### Output Text:
Pharmacological studies on a new <span class="chemical">dihydrothienopyridine calcium</span> antagonist , <span class="chemical">S - 312 - d</span> . 