4 Samhitas appear to be missing.
Vol 1: Text and Translation of the 20 Samhitas: Yajnawalkya Samhita, Harita Samhita, Usana Samhita, Angiras Samhita, Yama Samhita, Atri Samhita, Samvarta Samhita,
Vol 2: Katyayana Samhita, Vrihaspati Samhita, Daksha Samhita, Satatapa Sahita, Likhita Samhita, Vyasa Samhita, Parasara Samhita, Sankha Samhita, Gautama Samhita
About the Dharmasastra (from Wikipedia):
Dharmaśāstra (Sanskrit: धर्मशास्त्र) is a genre of Sanskrit texts, and refers to the treatises (shastras) of Hinduism on dharma. There are many Dharmashastras, variously estimated to be 18 to about 100, with different and conflicting points of view. Each of these texts exist in many different versions, and each is rooted in Dharmasutras texts dated to 1st millennium BCE that emerged from Kalpa (Vedanga) studies in the Vedic era.
The textual corpus of Dharmaśāstra were composed in poetic verses, are part of the Hindu Smritis, constituting divergent commentaries and treatises on duties, responsibilities and ethics to oneself, to family and as a member of society. The texts include discussion of ashrama (stages of life), varna (social classes), purushartha (proper goals of life), personal virtues and duties such as ahimsa (non-violence) against all living beings, rules of just war, and other topics.