diff --git a/include/xo/arena/MemorySizeInfo.hpp b/include/xo/arena/MemorySizeInfo.hpp
index 37b5ce0..a9649b3 100644
--- a/include/xo/arena/MemorySizeInfo.hpp
+++ b/include/xo/arena/MemorySizeInfo.hpp
@@ -5,6 +5,7 @@
 
 #pragma once
 
+#include <xo/reflectutil/typeseq.hpp>
 #include <functional>
 #include <string_view>
 #include <cstddef>
@@ -12,14 +13,27 @@
 namespace xo {
     namespace mm {
 
+        struct MemorySizeDetail {
+            using typeseq = xo::reflect::typeseq;
+
+            /** identifies a c++ type T.  See xo/facet/TypeRegistry **/
+            typeseq tseq_;
+            /** number of T-instances **/
+            uint32_t n_alloc_ = 0;
+            /** bytes used by T-instances **/
+            uint32_t z_alloc_ = 0;
+        };
+
         struct MemorySizeInfo {
             using size_type = std::size_t;
+            using DetailArrayType = std::array<MemorySizeDetail, 32>;
 
             MemorySizeInfo() = default;
             MemorySizeInfo(std::string_view name,
-                           std::size_t u, std::size_t a, std::size_t c, std::size_t r)
+                           std::size_t u, std::size_t a, std::size_t c, std::size_t r,
+                           DetailArrayType * detail)
                 : resource_name_{name},
-                  used_{u}, allocated_{a}, committed_{c}, reserved_{r}
+                  used_{u}, allocated_{a}, committed_{c}, reserved_{r}, detail_{detail}
             {}
 
             static MemorySizeInfo sentinel() { return MemorySizeInfo(); }
@@ -36,6 +50,9 @@ namespace xo {
              *  virtual memory addresses range obtained, whether or not committed
              **/
             std::size_t reserved_ = 0;
+
+            /** optional histogram with per-data-type counts **/
+            DetailArrayType * detail_ = nullptr;
         };
 
         /** function that visits MemorySizeInfo for a collection of @p n memory pools.
diff --git a/src/arena/DArena.cpp b/src/arena/DArena.cpp
index 72d8cbf..2cd36dc 100644
--- a/src/arena/DArena.cpp
+++ b/src/arena/DArena.cpp
@@ -176,11 +176,43 @@ namespace xo {
              *  must assume it's all used
              **/
 
+            // assemble histogram
+            MemorySizeInfo::DetailArrayType detail_v;
+            MemorySizeInfo::DetailArrayType * p_detail = nullptr;
+
+            if (config_.store_header_flag_) {
+                p_detail = &detail_v;
+
+                for (const auto & ix : *this) {
+                    typeseq ix_tseq(ix.tseq());
+
+                    // totals in detail_v[0]
+                    MemorySizeDetail & d = detail_v[0];
+                    ++d.n_alloc_;
+                    d.z_alloc_ += ix.size();
+
+                    // O(n) insertion here
+                    for (size_t i = 1; i < detail_v.size(); ++i) {
+                        if (detail_v[i].tseq_.is_sentinel()
+                            || (detail_v[i].tseq_ == ix_tseq))
+                        {
+                            MemorySizeDetail & d = detail_v[i];
+
+                            d.tseq_ = ix_tseq;
+                            ++d.n_alloc_;
+                            d.z_alloc_ += ix.size();
+                            break;
+                        }
+                    }
+                }
+            }
+
             fn(MemorySizeInfo(config_.name_,
                               this->allocated() /*used*/,
                               this->allocated(),
                               this->committed(),
-                              this->reserved()));
+                              this->reserved(),
+                              p_detail));
         }
 
         AllocInfo
diff --git a/src/arena/DCircularBuffer.cpp b/src/arena/DCircularBuffer.cpp
index e5b1c72..bd4dc0c 100644
--- a/src/arena/DCircularBuffer.cpp
+++ b/src/arena/DCircularBuffer.cpp
@@ -86,7 +86,8 @@ namespace xo {
                                    occupied_range_.size() /*used*/,
                                    occupied_range_.size(),
                                    mapped_range_.size(),
-                                   reserved_range_.size()));
+                                   reserved_range_.size(),
+                                   nullptr /*detail*/));
 
             pinned_spans_.visit_pools(visitor);
         }